Hi
I've just switched to Mac and Rename-It! is one util I really miss.
But there is some hope, it worked with CrossOver for OS X
http://www.codeweavers.com/products/cxmac/
CrossOver uses Wine and so you don't need Windows, but when I run Rename-It! on with CrossOver it lacks the system integration (you know right click to select files).
Yes this was a tip, but of course I hope there will be a porting of Rename-It! to OS X.