Had one phone interview, then met on-site with a small number of developers during a single day. All interviews were highly technical, focused on algorithm design, improvement, and ways to parallelize computation.
One interviewer was discourteous and impolite; when I misinterpreted a request, he was quite rude in pointing out that my answer was of a wholly different format than he was expecting. We did not get along, and as a result I did not fare terribly well. In every other interview, I believe I did very well or better.
Also, I really got along well with every other interviewer. In my limited experience, the reports of rude or dispirited Google employees are quite exaggerated.
I strongly suspect that a single mediocre report is enough to scuttle an interview, regardless of the others. My advice: Be prepared for people you don't get along with (as with any interview!), ask questions if there's even the hint of vagueness in your task, and have fun.