Loved working with lights-out brilliant people. Great place to spend a year; TW on your resume is a great door opener.
Pros
You'll learn alot - about technology, about yourself, about people.You'll learn at an incredible rate - mostly due to the smart people who will surround you. Of course - that will depend on the projects on which you get slapped. ThoughtWorks' approach to agile is better than that of any other company I've seen. When you travel, you're often with at least several others who are also traveling. Offers opportunities to socialize with colleagues in strange cities. Most ThoughtWorkers don't like Scrum. They prefer XP. This is good. Agile engineering practices are vital to successful implementation of agile. You'll learn this.
Cons
Travel can be onerous for those who want to maintain their personal relationships where they live (e.g. spouses, kids, friends). You don't often get a choice in where you end up. Fort Lauderdale in the winter? Great. New Hampshire? Not so much. You'll hear that you have a say in where you go, but you often don't have much of a choice at all. Flat hierarchy sounds nice, but can impart a significant political toll on your career. I know at least a dozen excellent folks who have been fired for various reasons - political, scapegoats for projects, folks not willing to violate their own sense of integrity to push company objectives that were incongruent with their values. Decide whether to fly under the radar, or challenge the radar itself. I know many current TWorkers who chose the former. I know ex-TWorkers who chose the latter. Politically, conservative views are poison here. There's a contingent there who thinks that Venezuela - under Chavez - was the model government. The predominant view is for bigger government. Contrary to the claim that dissenting/challenging views are accepted at the company, I've seen such expressions emit firestorms and tank careers. One very high level leader oscillates between saying he's a communist and that he's a socialist. If you're aligned with this - no problem. If not, consider staying under the radar with your views. Bill your hours to the client, then do your ThoughtWorks work. Expenses. Interviewing. Booking travel. Code Reviews for candidates. Working on RFP's. You get the picture. Be sure that you continue to bill your 40 hours though. Bill 60 hours on a project week after week? Not even an attagirl. Another integrity issue: SVIP.