Pros
Big Nerd Ranch has a lot of smart individual contributors, and there are often technically interesting and challenging apps to work on. You can learn a highly marketable new skill on-the-job, and the experience you get there is a great preparation for companies that are looking to hire software developers with a few years of experience. The work/life flexibility is hard to beat, the coffee is top notch, and the lack of oversight means there is very little in the way of sharp people accomplishing great things.
Cons
Several years into the merger with Highgroove Studios, the management doesn't get it, doesn't care about the people or the culture, and is really only interested in the bottom line. Perks are cancelled when there is a lull in consulting business, layoffs have happened only for hiring to pick back up the next month when work speeds up, and if you don't know what you're worth when applying, your offered salary will be a lot lower than other people there with similar experience to you. If you want to grow your career, you aren't given any direction or resources, and if you aren't teaching a class or writing a book, you probably should have your things packed.