O.K. here is my take on this: I work with both Macs and PCs.
Before we will start a war between Macs and PCs... this is just MY opinion
For laptops I would without a doubt go for a Mac and for desktops I would again without a doubt go for PCs...
I bought three MacBook Pros 13(!) inch with the stronger Processor 2.8 GHz and upgraded (!) from 4GB RAM to 8GB RAM.
a) I did not go for the AIR as I want a laptop with CD/DVD input. The air has none and you will have to buy an external CD player to either burn or play CDs
b) I went for 13 inch screen as I connect it at home to a bigger screen and IMHO the 15 inch and the 17inch are neither nor. They are not big enough to do serious PS work but they become to big to be easily portable.
c) I found the MacBook Pro better build than the Air. This might be wrong but the Air appears "flimsier" than the MacBook Pro
IMHO this is pretty much the best laptop on the market. I have also a Sony Vaio top end laptop that cost me more than the Macs but it is not of the same callibre.
Desktops: for my personal configuration a Mac would cost me an arm and a leg...I have 24GB RAM; the fastest processor on the market; th best graphics card and it was built to my specs. The same configuration with a Mac would have cost me at least double the price if not three times. Also, and this is a personal thing, I have a lot of free programs that are available for Windows but not for Macs. I would not want to miss them.
Last point: and this is a can of worms...I am not entirely sure about the future of Mac desktops...particularly since Steve Jobs is not there anymore...I think they are doing a superb job with all the iphones; laptops; ipads; ipods...but not so with their desktops. I will leave it at this as one can really start a long discussion about this...
Anyhow, I hope this helped a bit?