bensei said:Taking 20 requires some possibility for the character to judge how good his skill check was. This is not possible for Disguise, Forgery, etc.
Sorry, but I would have to disagree with you there. Why couldn't a forger just keep trying to improve his work until he's satisfied with it? Not having any artistic talent myself, I'm sure I could do a far better job at evaluating a forgery than making one myself.
Sure, if I needed to fake a signature on the spot, with witnesses watching, I wouldn't be able to take 20. But if I could practice all I want at home, I could easily take 20 times longer and produce the best fake signature I could possibly make. If I screw up on a single try, no penalty... I just throw that one out.
Of course, this all assumes I'm doing something where a failure doesn't mean some precious resource is being wasted. If I had to change a signature on a single existing document, one screw-up would be fatal (but I would have a good chance to realize I messed up, before I showed it to someone). However, if I were to forge a simple handwritten note (with some examples of the handwriting), the cost of failure on a single try is negligible.