Well I installed it on my iMac yesterday - upgraded from Tiger.
I have to say that despite the numerous and annoying interface inconsistencies, I kinda like it.
One thing that Win7 does better though is you can visually tell an application has minimized windows because the app icon changes to show 'depth' behind it - in SL the only way to tell you have minimized icons is via Expose.
I held off upgrading iLife to '09 however and will wait until likely iLife '10...
"Hi, I'm a young, hip, modern woman looking for a laptop for under $100. I'd like to have a Mac but I'm just not special enough for them. Hey look, I found this one on the bottom shelf at my local Walmart, the manual is in Chinese, but it's exactly what I'm looking for. Congratulations! It's a PC!"
The reason they aren't any viruses for Macs is the hax0rs all own Macs and actually like them.
That said it wouldn't take much to make a crippling virus targetting OS X - especially when they are the FIRST systems routinely cracked during the well publicized hacking contests.