Hey all,
I did it. I went out and got my 600D last night with a decent tripod and stuff but didn't get a new lens. Just got a single lens kit. Anyway, I was readying a blog post just before about taking pictures of the Milky Way (I wanted to learn the technical side not just 'Expose the ass off it!") and I found this post about the 600 Rule
http://blog.starcircleacademy.com/2012/06/600-rule/
Basically it states that the maximum length of an exposure with stars that doesn’t result in
star streaks is achieved by dividing the
effective focal length of the lens into the number 600.
Apparently the maths doesn't work out 100% when you get up the full frame sensors though.