We have an iMac. We've had it over a year, previously had always had Dell desktops. DH's dad has always used Macs (their home is like a Mac museum, is v funny) and got dh a Macbook a few years ago. DH then became a total convert and persuaded me to replace the desktop with an iMac when it was needing replaced.
I am so glad we did, it is WONDERFUL. From the very beginning it made me ooh and ahh just because it is beautiful.
I work from home part-time, on website maintenance-y stuff and I can have two full sized windows comfortably open and zip between them with ease. Plus my calendar and mumsnet. It suits dh too, some of his work involves a lot of proofreading and he can do it on the screen, 2 full sized A4 pages.
I have the wireless keyboard and magic multitouch mouse (or whatever it's called), they just WORK. I can zoom in and out of the screen, scroll up and down, all so intuitively.
As I say we've had it over a year, it has NEVER crashed, it updates software seamlessly, it's as fast as the day we got it, I can search through everything I have on it super-fast - I don't bother creating folders and filing stuff any more.
It's in a small room we use as a study but it also has a sofa bed in it - so when I am not working it's like a little cinema room, the screen is as good as HD (or better according to Apple) so we watch rented films from iTunes, DVDs, or dh and I catch up on iPlayer or 4oD. We only have one TV (with Wii attached) so this is a great extra and makes use of a room that might otherwise be underused. When the kids watch it we give them 'tickets' and they get popcorn etc which they love (they don't touch the iMac then! They do use it though, with supervision)
I don't feel I am using even 20% of its potential and plan to learn basic photoshop and video stuff to do so.
I can't really answer whether you need a desktop or laptop, but I would definitely recommend an iMac!
And you can now get Angry Birds from the Mac app store....