From a user point-of-view, there don't seem to be any new features in this release. It really is just a "hotfix" for a number of bugs, including the issue with Skype not letting other applications use the video camera that I affected some folks I know.
Anyway... Mac users who have gone ahead and moved to 5.0 may want to upgrade now (I have on one system and am still on 2.8 on another). The Skype blog post has a few more details on what was fixed.
P.S. If you haven't been paying attention to what's new with Skype 5.0 for the Mac, you may want to read about the "Gold" release, the launch of the beta of 5.0 for the Mac or my other Skype-related posts
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