For me it has been. I use one of the new imacs (upgraded to 3 gig of ram). I use a similar spec PC, with windows XP at work - (2 gig of ram is the only real difference).
The windows machine has a fit if you work over 300 DPI (which is high anyway, but standard for most A4 print work), struggling at times if there are lots of layers - forget opening any other application!!
When I got my imac - I had 1 gig of ram inside, it worked fine, I only upgraded becasue I do a lot of higher end video work (more than photoshop).
It IS an expensive decision, if you compare it to a cheap PC. The OS does take a little time to get used to, but not as much as I had thought.
Personally, I have just found my mac a total work horse. I often have firefox, photoshop, Itunes, transmission, adium and word open at the same time and it doesn't slow at all. Maybe i'm a lucky one, but mac has definitely worked for me.
Just be aware - your photoshop licence may or may not work on a mac - you will have to call adobe.