If you have copies of Office for the PC you can use them via Bootcamp (Mac's dual boot system) and its all pretty easy to use and run.
Unfortunately there isnt the range of cheaper software titles like you get for a pc, like photo editing software so you end up paying a bit more (unless you can get copies ) But they are releasing some cool stuff all the time...
Love the 24" imac, you may need to get a new keyboard as well as a mouse like AZ said, but also depending on your current router you may need to upgrade that too as the mac's will have the N spec cards... They will work on your current router but if you have a n router it will be faster... I think the current BT home hubs are N spec...
I dont have one at the moment but I am considering for Photo Editing and "Easy" computing as I dont use it for gaming, just need to get rid of a few PC's first!
Another major + is the Mac's ability to fit easily into your home AV system, get an Apple TV box and plug into any tv in the House and you can get to any music / video stored on your mac, and to extend, get a Apple Time Capsule you have a automatic wireless storage box...
And all the bits look great!!