It's up to you to decide. I like the Mac OS X myself, but not everyone shares that opinion.
It is true that the Mac has very very few viruses for it, and the only virus scan programs available are really just for misguided companies with corporate policies stating that all computers must have virus protection. You also get to avoid the whole malware mess with a Mac. Feature wise, OS X was what Microsoft was claiming Vista would be about 2 versions ago.
When it comes to compatibility, there's a Microsoft version of MS Office for the Mac, and it's really very nice. It won't read/write Office 2007 documents, and there's no Access, but other than that, it's pretty much feature for feature the equivalent of it's Windows cousin. It just has a much better interface layout that makes getting things done so much easier.
You also have OpenOffice which has the old X11 based standby, a new experimental OS X native interface build, and then there's NeoOffice for a more stable version of OpenOffice with a Mac native interface.
Most other programs will either have official Mac versions or something that will work just as well.
You can dual boot with Windows as well, or even run it in a virtual machine right along side your Mac desktop and apps. The latter requires a commercial program. Of course Windows will be just as vulnerable to viruses and malware running in a virtual machine on a Mac as it would on a PC, it's just the damage won't be able to spread outside the virtual machine on the Mac. So if Windows gets hosed, you've still got a working computer.
Learning OS X wouldn't be too difficult coming from Windows. About 90% of the concepts will translate directly. The rest would just take some getting used to, like learning to use the Dock or Expose (one of the single best OS interface innovations I've ever seen) to switch windows/programs, instead of the task bar.
Still, you might want to just spend time using your friend's Mac while you decide if it's for you or not. No point spending a lot of money on something you don't really end up liking. I personally dislike Vista with a bit of a passion. They screwed up a lot of the good things about the XP interface, and did a horrible job copying the good elements of the OS X interface. That's not even getting into the numerous technical issues with the OS. Like a bug that causes Vista to run out of memory copying files, and then failing to present the user with any kind of error message, just silently failing, and allowing the user to potentially lose untold amounts of data. There is a fix, but you have to specifically request it from Microsoft.
I thought I had decided to buy a laptop with Vista on it. I had even narrowed things down to the make and model series I wanted. A friend keeps trying to get me to buy a Mac instead. He said that his iMac gets no viruses (I find that hard to believe - less, of course, but none?) and that you can run Windows on it with the push of a button so there would be no work compatibility issues. I really hate the idea of having to learn a whole new operating system although if I bought a laptop with Vista, there'd be some of that anyway. He also said that whatever I do, don't get Vista. If I have to get a laptop with Windows, then I should get XP.
I'm so confused. Too many choices. I'd really appreciate your opnions on this.