You have to understand that nearly all cities were shitholes in 1989 until the Urban Revitalization of the late 90s. This wasn't an SF specific thing. NYC, for example, had over 1200 murders in 1992 (!!!) compared to last year's 414.

SF's revitalization has more to do with that than with "tech" jobs. I know in the Hacker News echo-chamber its hard to think there's anything but Internet Tech in SF but it's got ALOT more business than that -- It's the largest banking center on the west coast, got a massive bio-tech footprint, has some major apparel companies (Levi and Gap and a bunch of smaller ones), etc, etc. It's pretty diversified.