Sure, in brief: Smalltalk because we're most productive in it, Java for some code that particularly needed to be performant, and Ruby because it's better than the other two at interacting with the OS/tying all the pieces together. Obv JS for client-side whiz-bang.
Thanks.. you should be getting your results pretty quick (longer if you have a high-traffic site). Pricing is still an open question. We're talking about $5/month intro pricing for now, but presumably it will eventually be based on the traffic volume of the site/amount of data we're processing.