I have it installed on a Win7 & an XP machine as well as my Macbook and have not noticed any performance problems. I find it the most convenient way to deal with podcasts and audiobooks, not to mention loading my own movies and e-books without having to purchase from Apple.
I'm not trying to convince you, PhreePhly, I'm not a fanboy either way and everyone can do as they please. I just think people shouldn't be afraid to give it a try. It can always be uninstalled if it doesn't work out.
It runs pretty slow on my old MacBook (not pro), but I figure that's because I've got 15,000 songs on it. As noted, it's a nice, easy way to deal with podcasts and such.