Pros
The hiring process is ThoughtWorks' key strength. Everyone in a given project team are competent and motivated. The internal learning community within Thoughtworks is fairly good as well. There are a few terrific people (in every sense of the word) who contribute much more than they are given credit for. If you are lucky enough to work with one of these people, you will learn a lot.
Cons
Too many people are arrogant and cliquey. Management is increasingly either aloof or narcissistic. Be careful and don't get on their wrong side. Passive agression is a common trait unfortunately. Thoughtworks is no longer a great place to work at as a developer, unless you want to learn some basic XP. The glory days of cruise control and selenium are long gone. Innovation is considered risky at the consultant level.