Google actually had me do two on-site interviews (one in my hometown and one in Mountain View). The first one went very well. I had a great rapport with the (single) interviewer, and had fun solving the (single) problem he gave me.
The Mountain View interview went more or less like the one described in the article. Marathon style. Had good rapport with some of the interviewers, less so with others. Once you start stumbling your confidence starts to fall apart, and it can really hurt you for the rest of the day (the interview lasted all day).
I also didn't exactly end up with the job. They offered me a testing position with "fast-track" promotion to engineering. I passed on that.
Good advice in the article though: practice problems on a whiteboard at home or with friends. Especially fundamental problems that you learned in your first algorithms class and the like.