I used it from April '09 to December '09, which is when I got my Mac. I loved it, but don't get me wrong, I did have my share of problems.
Pros:
-It's not Windows
-It's free
-No viruses
-It's light weight, and doesn't have a CPU of 50% when sitting idle
-It's fast
-It has a nice interface
-I noticed my computer didn't get nearly as hot when I switched
And now for the cons:
-It locked me out three times, meaning it wouldn't boot up and I had to reinstall it after each time.
-There aren't a lot of known apps available for the OS.
-A lot of hardware isn't supported - I had problems hooking up a Lexmark printer.
-There were sound problems for a few months, my speakers would make crackling noises when listening to music or other sound. It mysteriously went away though
-When using youtube, or any videos for that matter, flash was slow and laggy
When you look at it though, no computer is optimized for that OS, which is probably why there are problems with it.
I'm not gonna lie though, I loved using it. It was a great experience after I had used Windows for so long, and I think if you can't get a Mac, it's a pretty close experience.