Facetime is one of my favorite features. I surprised my wife with a new iPhone 4 on Launch day, she thought I was only able to get one reservation, but I got two.
We use Facetime almost every day when both of us are at work. Works out especially good for me because I get no AT&T signal in my office, but I have full WiFi as I have an AP in my office. My Mom also got an iPhone 4 on launch day. We live 60 miles apart and we use facetime a lot. It was one of the features on the iPhone that I was kind of like "Ok, it's there but won't be very useful" but it's actually probalby my favorite feature of the upgrade from my 3G.