We replaced our PC with a Mac last Christmas and definitely not sure if I would do the same with hindsight, esp. bearing in mind the cost.
Pluses:
Very easy interface with all our other Apple gadgets, Ipad, Iphone etc
Virtually silent
Looks nice
Seems pretty reliable, doesn't lock up very often
Minuses:
Word for Mac is dreadful, doesn't seem to have half the functionality of Word for Windows
Some websites don't cope with the browser very well (have had to do an M&S order on the Ipad tonight because the website kept hanging up on the Mac), although this is fairly infrequent
I just can't get used to it. You don't realise how embedded in your ways you are with a PC, Windows, IE etc. I feel like I'm groping around in the dark still with Finder, which is the file manager function, it seems very unsophisticated. I keep finding little things it can't do which a Windows computer can, or it can but it takes you ages to find out how.
It tries to force you to do everything via Libraries which I hate (I know Windows is heading this way too).
Iphoto - I hate this and it is the default photo organiser.
The USB ports are round the back and not very easy to plug things in and out, you either have to go round the back or move it or grope about. We have ended up buying a USB hub.
Now maybe it's just me and I need to learn, but I am fairly computer literate and this just feels like a foreign language compared to getting used to a new release of Windows. I feel so much more at home with my work laptop and Microsoft.