Well, I don't know how much help I can be, but I "went to the dark side" about 2 months ago. I have been a PC guy all my life, but finally saw the speed and ease of use of MAC!
I got a MacBook Pro 15" with the i5 processor and 4GB Ram, 500GB HDD.
I am also running Aperture as opposed to Lightroom. I did run lightroom on my PC and found it to be a bit slow after adding many pictures. I have yet to see any slowdown with Aperture!
There was a bit of a learning curve from PC to MAC but the Apple.com website actually has many short tutorial videos geared specifically toward those of us "going to the dark side!"
Hope you make the jump...you will love it!