I never used voice chat in FFXI, because frankly the pace of battle was so slow that it wasn't even needed. That and nobody I was playing with wanted to use it, so it never was a point of contention.

In WoW, the guild I was in required it for raids just to listen to instructions. Most of the time my mic was muted in the 25 man stuff. In 10 man stuff I was a tank so I used it a bit more frequently then. After I got kind of close-knit with my 10 man group and some of the other members of the guild, I'd use voice chat a little more socially.

Going forward to FFXIV, most of the people I played with were from FFXI, so again, I never used it. The pace of battle was still slow enough that you could type out what you were trying to get across. I'm not sure how things will play out in ARR though. The pace of battle looks faster and more button-mashy, so it'll be hard to type in between abilities and moving around.