Yup, can confirm what people have said. My fiancee's family got us both iSights. I have 2mbps ADSL and she (in the states) has 512kbps DSL.
What blew me away the most was the sound quality, it's better than I get when I use skype to contact people in the states.
Video wise she gets 640x480 at around 240kbps 15FPS. I get the same except around 180kbps data rate. She's on a G3 iBook and it still looks great.
My only gripes are:
1. It won't let you do multi-person conferencing from a G4, which is odd cause when I have a single person it's only using like, 25-30% processor resources. I'm on a 1.5ghz powerbook btw.
2. No zoom, if you want your face to be bigger you have to move yourself or the camera.
3. Considering the price, i think it should use a 1024x768 sensor and down sample it, i mean, even my phone can do 640x480.
4. Not so much a gripe, but bear in mind you need decent lighting conditions. Natural light is best, otherwise i recommend pointing a bright lamp at the wall behind the monitor/iSight or else you get nasty shadows. Most reviews i've read suggest that those griffin light things are a load of rubbish.
So yeah, if you have the money, broadband connection and want to see your family then it's probably the best solution around.