That is only enforceable for Trade Secrets -- at least in most of the US. Google would need to prove that the things this employee worked on were "essential to the commercial viability of the business".
I totally understand not wanting to poke the legal behemoth, however.
As an anecdotal, a personal friend who is a former Googler signed a 10-year NDA, and he had his fingers in quite a few pies.
As I said, I definitely understand not wanting to be the one to actually set precedent - that involves getting sued by Google, which is expensive and potentially career suicide. But I think ultimately its probably not enforceable.
