It has been designed for teaching so there is a lot of material on their site geared towards learning. As part of that, it has a nice set of tools that make it easy to get started.
There are a lot of books that teach intro to programming in scheme so there is plenty of offline material as well. The little schemer, SICP, How To Design Programs.
It also has an active mailing list that is quite noob friendly.
EDIT: oh yes, and it is very a 'batteries included' environment. so you can worry about learning the language rather than getting your environment setup.
I also think Racket is a good introduction to Lisp. The documentation is great. Take a look at the vector documentation as an example http://docs.racket-lang.org/reference/vectors.html?q=vector&.... If you are not familiar with the language, there are plenty of examples to help you get going.
I recently started working through The Practice Of Programming and I wanted to compliment it with a functional language. I thought it would make the on ramp to functional languages a little smoother by first coding something in a language I'm familiar with and then port it over (producing more idiomatic scheme is the next iteration). I chose scheme as the compliment and PLT/Racket as the environment. So far, it has been working well.
