Quite a few questions about them. Intelligence boosts your amount of skill points, right? Is it retroactive, or you gain more skill points if you have higher intelligence earlier? (ie. it applies every time at level or just gives +# to amount of total skills?)
Now, just going over a list of skills to decide what's worth it (prepare for wall of text ):
Balance: In my understanding, worth it on melee toons... but do you really get knocked down that much? Is there any other use to it but to help when you get knocked down by enemy?
Bluff: I don't see it being worth it at all, although I have yet to try this on rogue. I haven't see many rogues use it though. How much more vulnerable are NPCs after this?
Concentration: I'm assuming it's worth it on any caster like wizard/sorc/cleric... since when you get interrupted, you still lose your spell points/charges if I'm correct.
Diplomacy: Mainly for rogues/squishy casters is my guess.
Haggle: Heard tales about haggle characters (transfer and sell) and my guess it's only worth on those ones.
Hide: Is it worth it at all on anything else but rogues?
Jump: IMO, the times when you need a high jump are so rare, why not just drink a jump pot and save points for something else?
Listen: How is it worth it if it only detects sneaking monsters? Besides, if you have high enough spot already, how is it worth it at all? Well, apart from random narrator comments.
Move Silently: I'm assuming it's mostly rogue only for sneak attacks... just like hide.
Perform: Only bard...
Swim: Completely useless with breath underwater ring they basically give you at start.
Tumble: Something I really always wanted to invest in, but been skeptical since heavy armor off-sets it pretty badly. It seems it's mostly melee characters specific... Is it worth it on heavy armor or only light/medium?
Use Magic Device: If I'm reading it correctly, most useful of all skills (maybe after spot). Is there some specific classes that don't need it though?
Heal: How is this useful at all?
Intimidate: Should be nice on all sorts of tanks... however every time I actually found it'd be useful, enemy couldn't be affected by it.
Repair: Same as Heal, how is this worth it?
Search: Pretty handy stuff, even on non-rogue IMO.
Spot: ONLY skill I found too useful to leave out. Maybe I just don't know dungeons well enough, but it saved my hide too many times... How high should it go to spot most of the stuff though? Should I just max it?
And the last one, cross-class skills cost more... so would you max Spot on a wizard for example, or you'd consider it not worth it?
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Sorry about too many questions, I'm a noob/newb at this game and I'm trying to figure out what is worth or not when creating a character. Feats/Enhancements are pretty easy since you can swap them out, though with some gold penalties. Race/Attributes/Skills are the only ones worth obsessing over for me now. I'm getting hang of first two, but the later is a bit hard to get right at the first time.