Among many, here's one of the lower-in-the-list upgrades in OS X Snow Leopard that I will be enjoying if everyone upgrades....
Having a video chat using iChat is more reliable and more accessible than ever in Snow Leopard. It includes technology to address many common router incompatibilities that can interfere with connections. And if iChat can’t make a direct connection, it will use the AIM relay server to create a successful chat session.
Now more people can have high-resolution, 640-by-480-pixel video chats, because the technical requirements are less demanding: You need only one-third the upstream bandwidth previously required — 300 Kbps instead of 900 Kbps. And finally, iChat Theater now offers 640-by-480 resolution, four times greater than before.
Full list is here
http://www.apple.com/macosx/refinements/
