[davidblondeau]

The main reason employees do not stick with companies as long in the Valley as in Seattle (or most likely anywhere else for that matter) is because a lot more people that work here want to start or join their own startup. And if they did not think about doing it initially, they will eventually get there since it is so much in the local culture.

[tikhonj]

I think it also helps that there are more options. You're much more likely to find somebody working on something you're really passionate about here than anywhere else, even if you're not actively looking. Not only are there more small companies, but (at least in my experience) everybody talks about interesting ones all the time.