So, how many have there been?
I'm trying to count up the number of OS versions (major and minor) since my G5 landed in my hands. It came with 10.2.7, and I believe that I went right to 10.3. (At least I can't recall if I installed 10.2.8 or not.) There were ten releases of 10.3, and now ten for 10.4. I believe that makes 21, with three OS reloads (I clean-install every major version.)
In all that time, I've had no major issues at all. In fact, the only real MacOS issue I've had in that time was at my former place of employment, when 10.4.3 broke NIS/NFS automounting on all the macs I administered.
Having started right at the preview release, I can honestly say that, at least in my case, OS X has worked well as a desktop system, especially since 10.2.It's not quite as robust as Solaris, but it's pretty darned good. Plus, Apple did a wonderful job with networking - many of the System Administrators I associate with have switched to carrying Powerbooks (now MacBooks), as they are wonderful for troubleshooting networks.
Hmmm, I've probably gotten off-topic, but since I've been crabbing a lot about Apple as of late, I thought I'd offer some props as well.