I ran an amnesia campaign once. It actually worked well, since I tend to be the only optimizer in my groups, so everyone got an effective character, even though they rolled randomly to see what they would get. I had made up 10 different PCs they could get, since I was unsure of the number of players who would want to try such a campaign. Then I handed out blank character sheets with only the alignment filled in, which I pointed out was not something they had to stick to, but rather is just an initial clue, as some classes have alignment restrictions.
First thing I did to help them learn what they were was let them sort through their gear, which held lots of clues. I think that's a big help, if you give them blank character sheets they have to learn to fill in. For the spontaneous caster, I let him make a few int checks to "remember" his spells known, while the mem casters just had to re-mem their spells instead. The others I gave clues about their abilities, as if instinct and training were kicking in, to let them learn. And later, after they "remembered" most of their stuff, I gave them the last of the unknown details, like unused skills that had ranks or feats that hadn't yet seen use. The players actually liked discovering what they were capable of that way, because it didn't force them to have to guess blindly, but still gave them the fun of discovery. Plus, they still had no idea about their backgrounds or histories, or even anything going on in the world, which gave them the freedom to really explore and be curious.
I also avoided giving anyone a class that had strict alignment restrictions, like paladin, because I didn't want the player to feel forced to RP a specific way. In fact, I generally play pretty loosely with alignments and how people should act in accordance with them.