hedwards: I think it's really one of the only reasonable positions to take. I dislike Windows and MS shows no particular interest in making a good OS, so I prefer to use something else.
Magnitus: I don't think Windows is bad quality per say. I just think they have their fingers in too many pies: browsers, word processing, servers, databases, software development tools and many more.
A lot of that stuff is optimized for their OSes in a way that only someone who has access to the internals can pull off and in many cases they don't try very hard for their products to mesh well with the competition either.
My preference for Linux is based on my desire to pick a custom combination of well optimized solutions that work best for me (for example, I'm not fond of C# and .Net for sever-side web development, I prefer some of the alternatives) and not have to pay however much Microsoft decides to charge me for them. In particular, it's also largely based on a desire to leverage more of the great things that are available on the open-source world.
I think if they didn't charge so much for copies, I'd probably not be so harsh on them. But, paying for the privilege of beta testing buggy software has never sate right with me. Plus the quality of the documentation hasn't been very good since they stopped shipping physical books with DOS.
Ironically, I really love their hardware and the lesser software products are often times quite good as well. I really liked MS Money, it's a shame that they gave up to the even more evil Intuit. If you think MS' tactics are questionable, Intuit makes them look like the patron saints of fair competition.