Vantaggi
You will work with smart people. ThoughtWorks' reputation makes it relatively easy to get conference and book proposals accepted. The company is very dedicated to improving the state of the art of software development. Work with people who have significant experience using agile processes in both the typical situations as well as those areas that other's know little about such as large (100+ developers) and distributed (across multiple continents) projects. You will have the opportunity to work internationally.
Svantaggi
Regular travel to boring places. Very hard to be exceptional in this crowd. Low compensation. Company is barely financially viable. International experience is required to reach the higher positions in the organization.