Integrated voice chat is becoming a default feature of many newer MMOs, and it's even been retrofitted into our older games, like EverQuest II and World of Warcraft. It's like power steering on a new car; you almost can't remember a time before it was standard. Games like Dungeons and Dragons Online were among the first to offer the feature, while others soon followed suit.
Personally, I find myself sticking with programs like Ventrilo or TeamSpeak to run my voice chat. Even in Lord of the Rings Online, I find myself turning off the IVC to use TeamSpeak with my kinship. So the important question here is: What do you prefer? Does integrated voice chat cause your game to lag, or any other performance problems? Do you just prefer Vent or TS (or Skype, or Xfire, etc) because you're used to it from before it became integrated? Let us know!