I had one phone interview and then an on-site interview for this position. The phone interview was a 45 minute technical interview including programming over Google Docs, and the onsite consisted for five 45-minute technical interviews (involving programming on the dry erase board), plus lunch. The interview is fairly challenging, so I would recommend reviewing any websites and materials that Google suggest you review, as well as maybe a combination of data structures, algorithms, and programming interview books.
I think it was difficult for me to gauge my performance in these interviews, as I got through the problems ok (with some hints from the interviewers), and the interviewers generally seem to be helpful to you. I did not receive an offer though. The interviewers were all polite, friendly, and helpful, and they all seem generally happy with the work culture at the company.