From an employee perspective I don't think it's really worth being outside London right now. I want to live somewhere where there are more than a handful of places that I could work locally (and I don't count companies bashing out websites in PHP etc). I'm not really interested in working for startups, but if I were I would definitely not move across the country for a single employer. It's just not worth the risk. It's sad, because I grew up elsewhere in the country and it would be great for those areas to have the same opportunities as London, but it is what it is.