I use it about 4-5 times a week on average about 60-90 mins at a time on my iPhone or iMac.
My home is in Modesto, Ca but I work in San Jose, Ca (90 mile difference) and also have a place where I stay at in SJ when I don't want to commute back home. So I travel and spend a lot of time between two cites and I have Family/Friends in both places, so I rely on FaceTime to stay in touch with them while I am away.
I feel that my conversations are different with people when I can see them, it feels more interactive and personal, like I can make them laugh more with my funny expressions (as I would if we were in the same room). I have a cousin with a 1 yr old baby and every time I FaceTime with her, the baby will be by her side and he sees me, so when i do visit in person weeks later he recognizes me right away and doesn't see me as a stranger.
You can't capture emotion over SMS or Phone Calls.
Those Ads from last year that showed the girl with a new hair cut, the young girl with braces or the woman telling her husband that she was pregnant, I feel that those ads were spot on and is the reason why a lot of my family and friends went out an bought an iPhone 4 or iPod touch.