[webwright]

Move now (assuming that you're audience/customer base isn't clustered elsewhere AND assuming that you're envisioning funding/VC).

Reasons:

-You'd rather deal with moving/visa issues before your startup launches.

-You'll have smarter startup geeks to talk to here, which will make your product better. Read: http://www.unionsquareventures.com/2008/06/the_spooky_econ.h...

- In the likely event that your startup fails (most do), you'll have had months of building a network which will help you find a cool startup to join or help spin up a new idea.

If you're going the lifestyle biz route, then you don't need funding and you don't need to be in SV (unless your target customers are startups).