It depends somewhat; if you're an avid gamer, you should go for a PC with Windows, eventually build one yourself or have it built for you.
If not, consider this; the Mac OS X has just come out with its 5th version in 7 years, while Microsoft came out with one version during that time. New versions of Mac OS X come in one version and you pay one price, so the day you want to upgrade, it is easy - and the OS is also cheaper than Windows.
The computers itself are more expensive, but not so much if you compare specs. But Apple doesn't have computers in the lower price range.
If you need to use a Windows-only application, you can do it on a Mac, but you will have to have a legal copy of Windows to be able to run Windows on the Mac as well. If you want, you can also run Linux.
When you buy a new Mac, it comes with a package of good programmes which in themselves are worth a lot. These are programmes for making movies, organise your photos, make music, web pages etc. and each of these are considered among the best you can get.
So far, Mac OS hasn't had much problems with viruses and stuff - well, although some alarms have been raised, there haven't been any real problems at all for users. This doesn't mean that it can't happen, though. Nothing is perfect in this world.
So, those are the pros. Now for the contras.
You will have to deal with a few incompatibilities, although not as many as people often claim. Office comes for Macs, too, and you can even use the free NeoOffice which should take care of that.
There might be web services which are very Windows-oriented and that may cause you problems, although it is becoming more and more rare these days. Having Firefox installed, helps a lot there.
If you use MSN a lot, the version for Mac is not so advanced as the one for Windows, but I've heard a new version is coming soon. For now, the Mac-version doesn't support audio and video-chat, but you can use Skype for that.
There might also be some problems with reading mail messages and attahcments between other mail clients and Outlook, but not much.
Last, Apple fanbois are not so bad at all:) Some of us are only glad to help if you have problems, too:)
But all said, it is of course also a question of money and you can get a good PC for less money and Vista is not so bad, I hear, although there are problems with drivers etc.
PS: gangster up there is coming with a few lies about Mac which it would be interesting to see some sources to. You don't have to pay a thing to use the OS, of course. What he probably is thinking of is the extended Apple Care Plan which you can buy if you want and not buy if you don't. You can also buy something which is called a dot mac-membership, but you would only need one if you have a little business or something and not even then. If you want to use iChat, you have to get a 2 months try out membership for dot mac, but after the period is expired, you continue to use your iChat-nick for free and Apple is not going to bother you any more about that. (I think they could have skipped that, too, but...)
If you want to use iTunes, you don't have to use the Music Store and you don't have to buy an iPod. If you want a mulit-button mouse, you can use any you like. It doesn't have to be from Apple. Same goes for keyboards or monitors etc.
But that is typical for the rumours spread about Apple's products, alas.