Edgewood said:
Do you actually go over a player's character sheet and find any glaring mistakes?
I never have before really. I don't care to spend my free time attempting to make sure that every i is dotted and every t is crossed. If they've got something wrong, well we'll generally cross that bridge when we come to it. I have always known/trusted my players enough under older editions not to bother - with perhaps one notable exception. When we went to 3.0 however we almost immediately went to the use of software-based character sheets and trusted them to be accurate and complete. Fairly recently I discovered that my players were so INSANELY dependent upon the software they actually had no idea how to level up a character anymore without prompts. That seems more unacceptable than having them actually do it themselves and get things wrong occasionally.
How about someone who has blatantly lied about having an item on her sheet when you know it wasn't there before? How much control do you place on a player's sheet?
Well you know that exception I mentioned above? One player back in the day had a tendency to keep notes - particularly notes regarding treasure - on a single, VERY worn piece of notebook paper. These notes were written at any and all angles, in no order, without dates, or additional data such as where a particular amount of money came from. When said player announced that he had approximately 1/4 million GP's the DM understandably balked and asked to be shown where it came from. When he saw the players clearly unacceptable methods of accountancy things changed a bit.

He let him keep to his claim of 250,000+ gp, but definitely required him to keep better records. He at least did BETTER after that although he never was particularly "trustworthy" from that point on as regards his characters money.
Aside from that renowned incident of questionable accounting practices I can say that I have never been involved in a game where a player deliberately lied about something on their character sheet. I've seen questions about how MUCH equipment was supposedly being carried, but not whether certain equipment was carried at all. Well, no I shouldn't say that. There's been a few times when players have questionably found yet another healing potion when it was absolutely needed (noticed because their conscience seemed to force them to at least mark off money to PAY for the magically-appearing resources). But it hasn't happened often enough to be important, and certain not for years now.
I don't place much control over a character sheet at all. I have occasionally asked to be provided with a copy and that probably goes as far as is necessary to keeping players from actually being deliberately decietful.
Do you go over them for accuracy or do you let the players do their own character sheet maintenance and upkeep?
Well when I've asked for them in the past it's really been to get a better idea of what they CAN do, not what they ought to be able to do or not. Since I stay out of how players divide the treasure among their characters I sometimes have no idea what I have handed out, what the PC's have sold or traded away, and so forth. If they want to "cheat" at D&D well they're ruining the fun for themselves more than anyone else. I won't take action until it starts interfering with the game in general or with other players enjoyment of the game.