I don't so much pre-order as I do reserve at the store.
The way it works in GAME (UK games chain) is that y'put down a deposit for the store to allocate you a copy; this also goes for limited or special editions, I guess it's not really advisable to do so, as it still means a guaranteed sale when the store orders the games, but it's something I would have bought on release anyway, so why not put down for a limited edition if I like the extras?
and I'm speaking strictly physical extras. That's pretty much why, because they're limited editions in which I like the extra shiny things.
I *did* pre-order XCOM last year, in the sense of paying in advance for it, didn't exactly have a negative experience, but I know it's not something to be encouraged. Paying in advance I mean, not XCOM. I loved XCOM.