Skype is suuuuuuuper laggy. Don't even get me started on how unnecessarily bulky that program is bgaatrtreanargle
I've had problems getting Teamspeak to work, but I know a lot of people use that for gaming chats. I've personally preferred ventrilo for group chats more than anything, mostly because it doesn't lag me to balls when I use it. (And I have a netbook, so that's saying something!)