My only regret is not doing so sooner.
Seattle is a wonderful town (and it really is a big town more than a city) full of wonderful, if slightly insular, people. It's beautiful, there's great food, you can hike and kayak if that's your thing.
If you're a developer that doesn't work for Microsoft or Amazon, though, the geek community is definitely lacking. There are plenty of professional nerds but much fewer people working on exciting side projects.
I found it much harder to meet people, nerds or civilians. It's the sort of place where people settle in, where people have grown up, where people aren't necessarily looking for new friends. All of which is fine, I just found it a bit off-putting.
Seattle doesn't really do urban density (granted, SF has plenty of room to grow, literally, here). Some of that is intentional, mostly it's just aggravating. It doesn't seem to want to be a city. Portland, which is smaller, manages to do many of the "city" things (like public transportation and urban planning) much better.
And, man. Don't forget the weather. Those months without the sun age you.
I loved my time and life in Seattle. SF feels more like home, even if I have to wait another year for Sonic.net to roll out fiber.