Unfortunately I don't have any huge insights. I've been using it on and off since 2005. It was recommended by a friend who lives in emacs. It makes lisp approachable and it makes me way way more efficient when writing and debugging lisp. No swank backend (and thus no slime) makes arc a hard sell. For those wondering what's so great about it - slime supports every major debugging feature I've seen in Eclipse or Visual Studio.
This is what I would recommend for someone learning slime:
If you are a complete slime n00b watch the screencast over at the slime homepage. I just watched it recently and it is well done.
I think the best way to learn from there is through using it to implement a non-trivial yet small project. Make sure the project isn't too challenging, so you have a chance to learn the new environment. Anytime you think there must be an easier/better way to do this - spend time learning slime. Keep coding and you'll continue to put yourself into situations where you can use slime in new ways.
If you have specific questions or problems it is worth asking the community or searching blogs / mailing lists. The questions are either answered already or someone will give you an answer. This is much like all the lisp and smalltalk communities.
I will see if I can get an expert slime user to post some more specific information. Maybe someone else can chime in. I know I have some useful information on specific parts of slime but it wouldn't help someone that is a new user.
