I can't say much about who the company is or what they do because its all under NDA however I can talk about what the place feels like. My first impressions were very "Silicon Valley". They have an engineering friendly organisation, so all the way to VP level you can earn the same being an engineer as you can being a manager. There was a fully stocked R&R room with iMac jukebox, TV, Air-Hockey, Pool table and the like. The average engineer age is 29, so I'd actually be old in comparison to the core workforce. The office is in the centre of town and quite spacious. The pension scheme is very good. The work patterns are flexible so commuting in on public transport would be very viable.
A few things do concern me. What they are trying to achieve is very ambitious and I'm not sure how I'll match up against the best of the best they seem to of assembled. The work would certainly be stretching, but I think that is a good thing, I couldn't be lazy. They work on very tight cycles so it could be quite high pressure. Although I can pull (and still occasionally do) long coding sessions my free time is still important to me. Its VC funded so its another risky move (although probably less so than leaving Marconi without a job to go to and then working for a small VC backed company).