eBay's Internet telephony division released Skype 2.0 for Mac OS X [1] today. The latest version, in testing for some months, brings video conferencing among Mac users or across supported platforms. That appears to be all that Skype is claiming for this upgrade from 1.5 to 2.0. Skype software is free, and version 2.0 is a universal binary; it's a 23 MB download.
Skype offers free computer-to-computer calling. Skype handsets have just started to become available for the same sort of calls, including Skype cordless telephones, which use a computer running Skype as a relay, and Skype Wi-Fi phones, which can connect to any open or simply secured Wi-Fi network to which you have access. Skype's computer software and handsets also offer fee-based calling into and out of the regular phone network, with free phone calls to the U.S. and Canada until the end of 2006.
[1]: http://www.skype.com/download/skype/macosx/