then why use it?

I don't use it on any of my desktop systems or servers. However, being a system administrator and a software developer means that I have to test things on it occasionally (as I must with every other Windows operating system). So I have to configure my "test box" (an extra system in my office with DriveImage on it so that I can reformat drive C with a new OS in minutes) with an XP image.

There are a lot of other things that irritate me about XP, but the fact that (as was stated before) the 3C509 is one of the most common NICs in existence, and it's not supported, is asinine.