Phone screen was good, done via Google Docs. All about trees. Interview consisted of several whiteboard-problem solving sessions; more trees, hash-tables. 6 interviews in total. 4 went well, 2 not so well. Last 2 were with people with very poor interpersonal skills... not sure if that was part of the test... I would not have accepted an offer anyway due to (a) location [Mountain View is very expensive, I found out while visiting], (b) office layout [everyone is crammed in to very small places], (c) attitude of last 2 interviewers.... What if one of those was my boss? And the food wasn't that great :)

Explain how a debugger works.