When looking for jobs, I'm not sure how to determine whether the company is fun to work for or not.

I want to work in companies that are open, innovative, and make a good contribution to the world of computer science.

For example, Dropbox looks like a very fun company and its existence is very important. How do I spot this in job advertisements?

EDIT: I should note that I live in Australia, so many of the fun companies that I know does not have any office here. I know only a handful of fun companies in Australia – including Google in Sydney. But I don't know that many.