The wife and I use it often. In this area there's a huge abundance of 802.11 signals -- AT&T and/or the cable company have a hotspot on nearly every street corner. Aside from that we both have Wifi coverage 100% of the work day.
We're likely to use it more as more family members receive FaceTime capable devices (the entire extended family is Mac-centric). My parents, for example, will have an iPad 3 once they're launched, and they spend much of their time in FL. They'll be able to see their grandkids (once there are grandkids) with ease despite being 1k+ miles away. Sure, there are other video conferencing solutions out there (Skype, Tango, etc), many of which are cross-platform and work over 3G. For our usage scenarios we don't need them to be cross-platform or 3G capable (have a hotspot for the latter, if needed, anyway). Relatively speaking, FT is much easier to use for the non-techy family members, and the video quality very good.