Interestingly, not everyone answers "tell me about yourself" with "what do you do." How someone parses the former can actually be more interesting than the answer itself. For example, some people answer with their family, their country of origin, their company (versus profession), their title (versus company), a description of their role, or–quite plainly–discomfort. (Crudely, I've noticed peoples' enjoyment with this question roughly correlates with their social competence, perceive social status and general curiosity about people. New Yorkers answer with a profession. Europeans, more frequently, with a town of origin. The oddest pattern I picked up on was in Montreal, where I kept getting a detailed description of what the person did or ate that day.)

It's also fun watching yourself answer the question, particularly when your parsing varies given the company you're with or context you're in.