Its always an entertaining conversation when a player pulls out a splat book for a specific class, race, etc. and shows me a rule for how something works, and I pull out the PHB or DMG and show them a rule for the exact same situation that contradicts what is in the specific book. This is far less common than the next wonderful thing I see happen alot more, which is.....
Its also groin grabbingly hilarious at a session, and this is more common, when someone asks about a specific thing they want to do, and no one can find anything written about it, but we all seem to know exactly where to find material in 2e, 3e, or 3.5e that shows the mechanics that should be followed to conduct that specific action. This is because the reverse engineered MMO on paper that is 4e excludes a huge amount of diversity in hopes to simplify the game to the point where it doesnt take eons to learn how to play it. Things got left out, and this is the first major edition this happened to, to this degree. We either have to go on assumption, or make a house rule, and usually that is based somewhat on the older mechanic in PREVIOUS EDITIONS, heh.