Hey Helen,
I'm a Mac user with LR and PSE8.
Like Audrey I haven't upgraded to Mountain Lion because I'm lazy and mean with my money!! Also, I'm fearful I'll have to upgrade my PSE again and I don't want to as I love PSE8 (after some initial teething problems) because it uses Bridge rather than Organiser and apparently later versions use Organiser. However, as a windows users you might find this better for you.
As to LR - it works brilliantly. Adobe products were originally developed for Macs back the dark ages so they work very intuitively even now.
Yes, when I switched from Windows to Mac I had to rebuy all my software, but in truth, I was running PSE2 when 4 or 5 was the current version so it really wasn't that much of a hardship. Buying MS Office was more of an ouch. And as Sara says, it can be very unstable and both Word and Excel crash regularly on exit, but I've learned to deal with this and save regularly!
It's not true when they say Macs don't crash. They can and do, but it does tend to be third party software that crashes (Apple created software is very stable - my Pages has NEVER crashed, but sadly I prefer MS Word as a wordprocessing package) and the crashes tend not to be catastrophic and take out the entire machine the way PCs are wont to do.
My Mac has never picked up a virus. Those irritating emailed viruses that do the rounds are just blocked and not allowed through. Love that!
I spent 10 years in the computer industry, using Dos & Windows based platforms and had never even seen a Mac before we bought one. The learning curve was very small - the close software cross is on the other side of the screen, that's about it! The file manager/My computer system is very straight forward and the search facility is simple, functional and WORKS. I sit down at Dominic's PC and I'm flabbergasted by the complexity of all the different drives and I can never find anything. And the close crosses are on the wrong side - bwahahahah!
Would I go back to a PC - absolutely no way.
Do I wish I'd splashed out and bought the really big screen - oh yes!