I'm a pretty big Eminem listener. I got Relapse the day it came out, it is really dark. This song is a solid example of just how dark the album is http://www.youtube.com/watch?v=v3hJqsgjtII
. However, I feel he works a lot out on the album. Listening to the tracks that come later and hearing him express remorse and give insight into his thought processes humanizes the horrific actions.
As far as being mentally screwed, it's known that he's OCD and ADD which would put him statistically at a higher chance of having some sort of depression. Depression is (at least I think) bio-polar to a lesser degree.
I don't feel that he is crazy though. He was neglected as a child and has become exceptionally famous over the last ten years. Which I believe has deranged his thought patterns leading him to do things that he didn't want to, further leading him to addiction because he didn't know how else to deal with the regret and guilt he was feeling.
The quote Jacker has given has been spoken in sightly different wording by just about every decently famous/good rapper ever. Just doesn't strike me as something that should give reason to assume someone is truly deeply psychologically disturbed.