Skype has rolled out HD videoconferencing for Macs--it's been available on the Windows platform for a while. Here at Design Nine, we just upgraded our own business videoconferencing software to include multi-party video. We use Skype videoconferencing daily for internal communications in our three geographically distant locations, which saves us money on our landline phone bill. We use Go To Meeting for client meetings, and find the screen-sharing particularly productive when trying to discuss something like a spreadsheet financial model. If you are interested in making more use of IP video, don't scrimp on the Web cam. We have found that the better cameras, with integrated, high quality lenses and microphones perform much better--plan to spend $80 to $100. You won't regret it.
Required broadband comment: If you want to make good use of the HD quality, you'll need symmetric bandwidth of at least 1.5 megabits. What does that mean? It means it won't necessarily work as well with asymmetric services like DSL and cable modems.