In Americas Army (that FPS) you can turn on a Text To Speach option for ingame chatter. Quite cool as an extra if the quality isn't an issue. I wouldn't use it for anything else though, even the best computer generated voices sounds ugly compared to real ones.
It would of course be quite interesting for RPG which usually feature lots of text which makes it almost impossible to have them spoken (both time as well as budget wise). Although, as far as I know the Gothic games had that (all the talking by NPCs was spoken).