I read quite a good interview with Chicken Scheme's author a few months ago. Here's the link which might be of interest:

http://spin.atomicobject.com/2013/05/02/chicken-scheme-part-...

It depends on how you use Racket, since it is actually a family of languages, but if you use R5RS I would say it should be really easy to port apps between them. And the community is great so I don't think you would have problem picking it up