The problem with this approach is the FLOSS stuff being more interesting ends up impacting the success of $work, or the $work distracts you enough that you can never focus long enough on the FLOSS. Plus the guilt.

Plus, at Google in particular, you have to make them aware of your OSS work and go through the motions of getting the licensing set up so either they own it or you get permission.

Even if you "get permission" that's only for copyright. They still claim ownership of other IP (patents, trademarks, trade secrets), ... on _everything_ in your private life. I doubt it gets enforced often, but the employment contracts are draconian.

I'd say work on an existing project they can't wrestle control over. I am not your lawyer however.