I don't think I have to explain the difference between live testing, and this.
Have you tried Expose feature for Mac? It's really great for multi-tasking. It took me a while to get used to. I love my dual monitor PC for multi-tasking but Expose really keeps me organized.
Yes (I have a Mac as well) and clicking a button by glancing my eyes down will always be faster for me than searching for a function key - finding my window - moving to it - etc. Especially when using a program like Photoshop; where OSX tosses everything all around the screen instead of keeping it in a nice little box for me.
I work faster on a PC. Mac's are boutique, and good for the simple things.