Disclosure: I worked there for four years and interviewed a lot of people.
I decided to take another offer. I'm sure google's offer would have been great, but the timeline was taking too long, and I wanted to start at the other place, so I didn't wait for it (2 weeks at that point).
The bottom line is that, unless you request everything to be expedited from the beginning, it can take a few months to finish the entire process with Google. Even requesting a schedule change to be made would take about half a week for me. At least that was my experience -- I can't speak for others.
That is not too bad for such a large company really. Personally I have always worked for small software companies where the hiring process frequently consists of one interview, a bit of a programming test and an offer all concluded in 72 hours (frequently less). Compared to that a few months seems slow but I once had a friend get hired as a trader at a huge international financial organization and that took a glacial 6 months.
Whats more there was the expectation that you would more or less just walk out on whatever job you happened to have accepted in the interim, get on a plane and fly to where they wanted you as soon as you finally received an offer. Looking back on it I suspect that agreeing to that was itself part of their selection criteria.