For some head-scratching reason, Skype didn't mention a major upgrade to its recent Windows beta when it dropped in early December. That would be the ability to make 720p, HD-quality video calls if your video hardware supports it.
No word yet on a Mac (or Linux) release with HD calling yet, and PC World guesses they wanted to make the announcement at the Consumer Electronics Show, next to news about HDTV integration. I discovered the video boost, in hindsight, after recording a recent TV news appearance, so I can testify to the beta being worth an early upgrade.
Skype's 4.2 beta is a free download for Windows systems only. If you're seeing HD-quality video on your Skype beta setup, tell us what camera is giving you the good stuff in the comments (I was using this Adam-recommended Logitech 9000 during my brief video interview).