Very little of the work done on Google products is directly assigned by Google management. I just finished up a week-long demo that fixes a longstanding annoyance with the search results. I saw a need, made a quick 10-minute screenshot mock-up, gave a 3-minute presentation, recruited a few co-conspirators, and we built it. Management will be involved in the decision whether to productionize and launch it, but the demo was all done at the individual-contributor level.
I've got a 20% project that, to my knowledge, my manager doesn't even know about. It grew out of my 80% project - we needed a library that doesn't seem to exist yet. When it gets to a semi-functional state, I'll open-source it through cdibona's office, with copyright assigned to Google. Why not? It'll end up exactly the same for end-users, with an Apache license, and it's much less of a bureaucratic hassle to just do it with a Google copyright.
None of that is related to cookiecaper's point though. Your project is obviously related to Google, used Google's resources and engineers, and was in response to a problem that Google had.
The point is that Google will claim copyright of everything that you do. If you write a game about chickens in your spare time, for example, then Google owns the copyright, despite not having had any input into it. I fail to see how that's fair or reasonable, and I'd be very interested to see what laws apply - I suspect that cdibona is trying to blow smoke up our collective asses.
In your case it makes sense; you wrote the library at work. Google paid you to sit in Google's building using Google's computers and networks to write the library. If they want to own it, it's not unreasonable at all.
What is unreasonable is that if you did it at home, with no Google resources, that they would still ask you to assign them ownership.
(I, fortunately, don't have this problem. Part of the official open-sourcing process involves deleting any reference to our company, even in the copyright, so that nobody sues them if it breaks. Example internal app that was open-sourced: http://openefs.org/)
Why does my physical location make a difference? I'm free to go home as I please during the workday. If I duck out of work at 3 PM so I can go home and use my own laptop to work on a personal project, should it not be owned by Google? If I work on it in the mornings and come in at noon, should it not be owned by Google?
Well, obviously before that phraseology goes into a contract it would need more refinement. A better term is probably "Any work not performed in the course of regular employment duties", or something like that. The point is that Google should not be claiming copyright on things that they have nothing to do with.
I've got a 20% project that, to my knowledge, my manager doesn't even know about. It grew out of my 80% project - we needed a library that doesn't seem to exist yet. When it gets to a semi-functional state, I'll open-source it through cdibona's office, with copyright assigned to Google. Why not? It'll end up exactly the same for end-users, with an Apache license, and it's much less of a bureaucratic hassle to just do it with a Google copyright.