I used to hang out at c.o.l.a (comp.os.linux.advocacy) when I was still a Linux fan. There are just tons of flames between the Linux and Windows camps ('cause they usually cross post to comp.os.ms-windows.advocacy). There are quite a few truely knowledged people from both camps, and it's fun to read their posts.

So just pick a topic you like and hang out there, you'll learn a lot from it. Believe me.