I have both a PC and a Mac, both of which have Photoshop. I've found that the mac is so much easier to work with, the format is nice and it can handle multiple huge files without slowing down which is important for me since I work so big. Also, this computer has never crashed on me but my Windows would always crash a lot when I had spent 5+ hours on a drawing I didn't save. I also love that the graphics are so much clearer and detailed on my mac. I was always disappointed when I transferred an image I was working on my PC with over to this computer because the colors would be kind of gross. So I've found macs so much better to work with with Photoshop.
After falling in love with the Macs at school, I got a Mac when it was time to replace my 6 year old HP laptop. I use Adobe Illustrator CS5 and Photoshop CS5. So far, there are absolutely no regrets on that switch.