Persoinally I hate using in-game VoIP because it usually always sucks bad... I prefer using something like Ventrilo or (to a lesser extent) TeamSpeak as you have benefits of:
1. Better ping rates in the game... there's nothing like some gimp screaming in to his mic and causing packet overload due to faggotry.
2. You can have private conversation with people you choose to talk to rather than a bunch of anonymous people who are probably annoying anyway.
But either way, I guess it could prove handy to have some kind of VoIP support... especially if you wanted to make your own "ventrilo" type of program.