Cut and pasted, since the forums lost it and somebody ran a cache search on it. I don't want it to disappear on us again.

Introduction
This guide is a consolidation of answers to some frequently asked questions about the 'big 4' rogue skills (Disable/Open/Search/Spot), including: how can I boost my skills? How high do Trap/Secret Door/Lock DC's go? And other assorted questions that frequently come up in the rogue forum. What I *won't* try to do here is exhaustively document the DC of every trap, door, and lock at different difficulty levels; that's simply too hard to keep up-to-date when those values occasionally change!

Ranks
I won't get into build recommendations too much here, but I will give this one -- if you're a pure rogue, keep max ranks in Disable Device, Open Locks, Search, and Spot (level+3 ranks). If you're a multiclass, you may be doing some optimization and let a few skills lag behind, but I'd recommend trying to keep close to maxed as a multi-class, too.

Current max ranks: 17.

Items
Note: Only the highest item bonus will apply amongst items you have equipped.
Randomly generated items give +1/3/5/7/10/11/13/15 to any skill. Some named items also give a small "Luck" bonus, which will stack with an item bonus.
See this thread for a detailed inventory of known static/unique items in the game, and where they can be found.

It's reasonable to assume that you can find/buy a +13 item for nearly any skill on your way to level 14, with sufficient time spent browsing the auction house. So, for those following along at home, we've got a base of 30 points -- 17 ranks + 13 item bonus -- that will be relatively achievable by nearly any rogue build. Even many of the multiclasses with only a few levels of rogue can usually find a way to get in this neighborhood.

Tools
I advocate working on your Free Agents favor early, as the purchasable tools give you a *significant* guaranteed boost to Disable Device and Open Lock.

Rusty Theives' Tools: no bonus
Theives' Tools: +1 Open and Disable**
Masterwork Thieves' Tools: +2 Open and Disable**
+1 Thieves' Tools: +3 Open and Disable***
+2 Thieves' Tools: +4 Open and Disable***
+3 Thieves' Tools: +5 Open and Disable****
+4 Thieves' Tools: +6 Open and Disable****
+5 Thieves' Tools: +7 Open and Disable

** - purchasable from a vendor
*** - purchasable from Free Agents rep at first rank
**** - purchasable from Free Agents rep at second rank
Look at this thread for info on how to most easily get the 150 favor needed to unlock +4 Tools.

So long as you make sure to hit Free Agents quests, you're now tracking to a 'guaranteed' total of +36 for Disable and Open rolls, and 30 for Search and Spot, before making any significant build decisions. Add in an unlimited supply of Heroism potions (easy enough to afford when you need them), and you're working with a base of 38/30 before making build decisions.

Tradeoffs
Here's where things start getting interesting, with different builds going in different directions. Simply having max ranks, upgrading your equipment when you can, and getting Free Agent Favor/Heroism potions will enable you to be sucessful with 90% of the game's content on Normal. To expect to have success on Elite, some additional investment will need to be made in the form of feats, enhancements, good ability scores, and buffs from other players.

Feats
All feats stack.
Nimble Fingers - +2 Open, +2 Disable
Alertness - +2 Spot (and Listen)
Skill Focus: "*" - +3 to * (Disable/Open/Search/Spot)

Enhancements
Enhancements stack. (Note that while the Rogue, Ranger, and Human action boosts would theoretically stack, they are both on the same recharge timer, and can't be launched at the same time.)

Rogue/Skill [Disable/Open/Search/Spot] I/II/III/IV - +1/2/3/4 to Disable, Open, Search, or Spot
Rogue/Skill Boost I/II/III/IV - +2/3/4/5 to all skills (but unlikely to be used for Spot), 20 seconds, 5/rest

Ranger/Skill [Search/Spot] I/II/III/IV - +1/2/3/4 to Spot or Search
Ranger/Skill Boost I/II/III/IV - +2/3/4/5 to all skills (but unlikely to be used for Spot), 20 seconds, 5/rest

Drow/Skill [Search/Spot] I/II/III/IV - +1/2/3/4 to Search and/or Spot
Dwarf/Skill Search I/II/III/IV - +1/2/3/4 to Search
Elf/Skill [Search/Spot] I/II/III/IV - +1/2/3/4 to Search and/or Spot
Human/Human Versatility I/II/III/IV - +2/3/4/5 to all skills (but unlikely to be used for Spot), 20 seconds, 5/rest

Attributes
Int modifier: +modifier to Disable, Search
Dex modifier: +modifier to Open
Wis modifier: +modifier to Spot

Buffs
(In most cases these will come from outside sources.)
Competence bonus:
Bard/Inspire Competence: +2 all skills (never self-applicable)
Morale bonuses (do not stack with each other):
Heroism/Good Hope: +2 all skills
Greater Heroism: +4 all skills

High Water Marks
How high do DC's go? This frequently changes, but the highest known DC's in the game are currently:

*Stupid Cabal Trap*
(This trap guards a single chest, and has DCs on Elite that are silly-high enough that your party won't expect you to be able to disarm it -- all they lose is a chest, and the DCs are simply too high for all but the most trap-optimized builds to achieve.)
Disable Device: 73-76 DC.
Search: 61 DC

*Everything Else*
Disable Device: at least +56 modifier for 100% success. Aurum Lair trap with DC at least 61.
Open Locks: +32-36 modifier. First locked chest in Twilight Forge, has been failed on a total 51, and succeeded on a total 56.
Search: ?? (traps)/ 45-48 (secret doors) VoN 4 secret door has been reported as 45-48 DC on Elite. Second highest trap (after Cabal) in Gianthold has not been discussed.
Spot: 35-36 Maze of Madness, Cry for Help, Feast or Famine on Elite requires a Spot of 35 or 36 to spot traps.

* - I use 'modifier' rather than 'skill' on Open and Disable because the Tools contribution will not be reflected on your character sheet when you look at your skill tab, but will only be added into the modifier at the time of the die roll. Note that also due to the die rolls, I've cited modifiers below the DC's -- in the case of open locks, you can reroll until you get a 20. In the case of disable device, you can reroll until you get (DC - 5) or lower, at which point the trap blows, so a modifier 5 under the DC will always get you the trap eventually. Slightly off-topic, but important to know: you will use whichever tools are "first" - ie, top left corner, first inventory tab is your 'first inventory slot'.

Must you meet all of these DC's with your build? No. These numbers are listed more as a reference to know when to quit raising a score! For example -- the highest DC lock (that's currently documented) can be opened with 17 ranks, a +13 item, +4 tools, and *nothing else*. So, you may not want to invest any feats/enhancements into Open right now, until someone identifies a harder lock to pick!

Can you decide to try and build with getting 100% success on all these DCs? It's certainly possible with some builds, but requires a heavy feat and enhancement commitment. Like every build decision, it's a trade-off. What I'd suggest is to look for which ways you can most efficiently raise your scores with enhancements. The most action-point-efficient ways are with Rogue Skills Boost and Way of the Mechanic. (Although Way of the Mechanic comes with a fair amount of prereqs -- you may be taking most of them already!) Early levels of skill-specific enhancements are cheap, but by the time you get to level IV, getting another +1 to all 4 scores requires 16 AP, a *huge* cost! As with any build, decide what your goals are, and what tradeoffs you want to make to achieve those goals.