New Safari and Firefox Mac browsers now include the OS version in their user agents. For instance, Safari 3.1's UA is:
Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_5_2; en-us) AppleWebKit/525.13 (KHTML, like Gecko) Version/3.1 Safari/525.13
Firefox 3 beta is:
Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9b4) Gecko/2008030317 Firefox/3.0b4
It would be great if we could start differentiating between Mac OS X versions. Note that Firefox 3b4 only reports the major version while Safari 3.1 reports the major and minor version. Hopefully we can get the Firefox guys to add minor version reporting before 3.0 is officially released.
Thanks for considering this feature.