It is also used by Y Combinator (Hacker News is programmed in Arc and the Arc language runs on mzscheme, which is Racket's core).

Last year, someone from Naughty Dog gave a talk at CUFP about using Racket: http://cufp.org/conference/sessions/2011/functional-mzscheme...

Don't know of big companies, but it used to be called PLT scheme. It's known for it's huge-ass standard library (batteries included style) and being used as an educational tool in a bunch of big tech schools in the US.

Not a big company, but Northeastern University's CS department uses it in their intro course to computer programming. The staff there is all about PL research and I believe they use it pretty extensively in that regard.

I spent a semester there and the staff are hardcore into it. I learnt a lot from Olin Shivers (http://www.ccs.neu.edu/home/shivers/) and he used Racket extensively.

You know that "Racket" is the former "PLT Scheme", right? Some boutique consultants use it, notably Untyped: http://untyped.com/

It's also used at the University of Waterloo in Canada for their first few CS courses.

I don't know of any (and I dont think there are any), unless you accept major educational institutions as a substitute for big companies.

I keep waiting for Racket's day to come, because it is a really great system.