Apple brought out the Mac OS X public beta around September 2000. Back then, the Carbon application library and compatibility layer didn't function well, so they allowed a lot of the old Mac OS software to work on Mac OS X.
Yahoo! Messenger was one of those and I ran version 2.8.3 for the longest time. Around 2005, Yahoo! announced the version 3 development project and the first two beta versions were rolled out that year. After the second version release, I joked that they would finish in 2011.
There were two each year until 2009, when they released four beta versions. I believe the same year, they increased the version number to 3.0.1, probably to make someone feel good, while they were popping out iOS versions right and left. (Who says that Mac OS X and iOS are related?)
Just a few minutes ago, I saw Yahoo! Messenger version 3.0.2 (no beta!) show up and I'm running it now. It looks very much the same, and really isn't that much different than 2.8.3 but we can hook up with MSN Messenger users--something else that's been somewhat neglected. Besides that, the Buzz! feature has been working since 2005. It's historic, or at least, hysterical!
Well done, Yahoo!