I went to college in the UK. Before, during and after, I worked at a series of startups. I gained experience in PHP, MySQL, etc.. -- a slow but steady accumulation of skill. Then I got a job with Yahoo in the UK, who despite their (many!) flaws as a company are a world-class web development organization -- I learned more, but at much the same speed.

After a year, Yahoo moved me to the bay area, and the difference was shocking. The demands made of me professionally, the density of smart and talented people everywhere, the intensity of the focus on tech culturally and socially: it blew me away. I went from feeling like a spectator of internet technology to a participant at the leading edge -- in terms of the skills I had, the people I met, the sense of the industry's direction.

The bay area is where people invent the next big thing, continuously. London has improved substantially as a startup environment since I left, but it's still nowhere near the same league.

Let me guess. In the UK you are promoted based on years of experience, in the US based on competence.