My Father and I both use iChat AV weekly to talk to my sister and family in Melbourne. Sometimes the video from Australia goes blocky, but that's down to their upstream speed on a 256K connection. We both have 2Mb BT Broadband here in the UK, and our transmission is always excellent.
I set my brother-in-law's iMac G5 up before they moved out there with an iSight, then he just plugged it into a broadband connection and we've been 'seeing' each other just fine vere since.
As with most things Apple, 'it just works!'
Nig.
The iChat AV Resurrection