Hopping after 6 months, or say less than a year, will definitely hurt your resume, even in the Bay. As a hiring manager, I'll typically assume your either got fired, or gave up too quickly. Both strong reasons not to hire you.

Hopping after 2 years in the Bay is extremely common. So much that I'm not even sure it's considered "hopping" anymore.

I'm not sure how long of a time horizon you mean when you suggest job-hops will eventually hurt you. In the Bay, at least, if you have say 5 2yr stints, what's likely to hurt you is... your age.

A developer with 2 2yr startup stints is your typical Bay "senior developer". And a developer with 1 2yr startup stint is your typical "experienced" Bay developer, and generally one of the most in-demand categories of developers in the Bay.

I'd go so far as to say that the 2 2yr stints will look better to a startup hiring manager than 7 years in an corporate environment like Oracle. The former is definitely in tune with SFBay startup-scene vibe, the latter looks like a corporate potato whose fit for startup life is questionable (not to mention a little too old as well ;).