Just to add MY anecdote…
I swear by OTC generics. I’ve always been okay with prescription generics, never noticed any issues, until I recently spent a spell on Wellbutrin. WB has multiple generics of bupropion, including one common one, Budeprion. The Wikipedia entry mentions problems with the generics; it says the FDA resolved them, BUT…
I hate 'em. The name brand never gives me any trouble, but when I’m taking the generics, I can often tell that something isn’t right. I’m not sure if it’s a dosage thing, a delivery thing, or whatever, but even though I’m happy to take the (cheaper and insurance-covered) generics, there’s definitely something going on there.
Anyway, my point is: there’s no reason generics SHOULDN’T be identical to the name brands. Alas, in practice, different manufacturers can have different quality control standards, and in some medications, that little difference can not only noticeable, it can be significant.