Here's some more to chew on,
http://venturehacks.com/articles/job-offer
http://genuinevc.com/archives/2005/10/18/seven-questions-emp...
http://blog.guykawasaki.com/2006/03/nine_questions_.html#axz...
Short advice: Go for it, but approach with caution.
1. If you are young free and single, hell yes. Having no life commitments is not something every young person finds, and much rarer as you start to go grey. So take the opportunity now if your life fits well. (I am reminded of a poem to the poets younger self, about running barefoot more often, sleeping around more. Those I leave up to you )
2. The whole career stability thing - there was a recent post about recruitment agencies and another on the non-existent skills gap. In short large companies used to hire right out of school, mentor, train and churn out well rounded professionals. They stopped doing that.
A start up is the most likely place to get ten years corporate experience in 2. Maybe. Whi h leads to 3.
3. It totally depends on the start up itself. Gut feel is the best I can suggest.
But if you life circumstances can support it, take a flyer and join one. Worst case you are looking again in 6 months but with some intensive experience under your belt.