Kwaad said: you can fit around 50hours of audio in 1gb. 25hours of audio in 500mb. and more like what would be in a game. 5hours of audio in about 100megs. I promise you, Text to Speech will never sound as good as a real voice actor.
Yes that's fine and lovely and let's just pretend that voice actors are free. that's an exepensive process, and what's more important in regard to text to speech is that you can't tell the game to say something. For example I created my own player in 2k7 MLB and of course he's the only guy on the whole team where the voice anouncer doesn't say his name. That's where text to speech can be implemented.
Secondly text to speech is old, but the old technology you speak of his horrible. I know Microsoft not to long ago had a big project working with a major linguistic professor, attempting to get an artifical voice that actually doesn't sound like a robot talking. Believe it or not speech synthesizers have been around longer then you think, they showed the VODER in the 1939 World's Fair. But obviously there is room for improvment.
Another element to speech synthesis, is implementing it into AI it' definitly a next-gen feature, imagine playing a shooter and you yell things in the mic at people like, "your going to die punk!" Then someone asks you what it means, and they repeat the expression, and the AI learns to use this taunt and later you hear them yelling it to you in their own voice, and perhaps even rewording the taunt. A better way the voice synthesizers work is with singing, they can even make it sound like a whole choir is singing something. Imagine Kwaad is playing a shooter and he gets a head shot, and the music in the background you here the choir roar, kwaaaaad, kwaaaad, anther one dead, a shot in the head beware...kwwwwaaaadd!!! Just something silly, the point is it gives you unlimited options, and since the AI can change the pitch and tone of the synthesized voice is can mix it on the fly to the music's beat and rythem. Just imagin a rythem game doing the name game and you get to input your name and synthesizes it into the song. It really has amazing prospects.