Have you ever used the Mac before? If not, I would recommend heading over to the Apple Store and test drive a system. Consider that you're using a computer that is being used by everyone so expect some issues from other users (the ol' ID-10T and PEBKAC issue
). But at least this way you can get a feel for OS X and the Macintosh.
As for software availability, I guess you can say that Windows has more software available for it but how much of that software is actually useful? The majority of the stuff out there is a rehashing of a major product that actually has a Macintosh equivalent, sometimes from the same company that makes the popular product. Same thing when it comes to games, but this one doesn't hold as much water. Even still, the top billing games usually have a Macintosh port, even a Linux port.
As for general usage, anything that you'll find on the Windows side you'll find on the Mac side. Be it a direct port or a great equivalent to what's available on Windows, you'll find it for the Mac especially if it's an open source application.
One thing to note: Don't treat OS X like you would Windows. If you expect to use OS X like you use Windows you'll be extremely frustrated. If you want Windows, stick with it. Otherwise, open yourself to the way of doing things on the Mac. This is what I've done with Windows and Linux considering that I started on the Mac, and I've learned a lot from all the platforms to make a well-balanced decision about each of them.