Since I found chicken scheme I have used it do everything I can. I have built numerous web applications using it and it always makes my happy inside; something I can't say for other ecosystems. It also works great for scripts and interfacing to system libraries.
And of course the community is amazing. Even when I was new to lisp and chicken my questions and patches were always taken seriously and responses are always kind and helpful.
As felix mentions chicken scheme is really fast. Even on websites with moderate load and very little performance profiling or caching my dynamic pages are very consistently generated in less than <20ms. If you go a bit further and give the compiler hints it gets even faster. And if it isn't fast enough yet you can embed C code straight in your lisp source files.
It is tough to beat a language and ecosystem that nearly never gets in the way, is easy for rapid prototyping, and gets great performance when you need it.
As mentioned, Henry Bakers "Cheney on the M.T.A"[1] is a great read. I have used it to implement a scheme system as well.
In summary: use chicken scheme if you want a nearly mature, production ready, rapid prototyping, statically or dynamically typed, fast, easy to use, and powerful language and ecosystem.
edit: Another really cool feature of chicken scheme is the ability to serialize continuations. It can be used to make an extremely powerful stateful web app that operates like arc and hacker news.[2] Since you can serialize the continuations you can write the state to a file and you won't lose the state when you restart the app or the server crashes.
[1] http://home.pipeline.com/~hbaker1/CheneyMTA.html
[2] http://wiki.call-cc.org/eggref/4/suspension and http://www.paulgraham.com/arcchallenge.html