If it is a good offer with a well-established company, what sorts of risks are you taking with that?
I know. Not much except that I have to move there and risk their business don't drop 50%. The other risk I am taking is I am leaving a comparable company in Canada, but a intermediate position.
Based on that, I would say that it is worth it. If they are offering you a job right now, it's not likely that they are considering cutting it any time soon. SV is a great place to be if you want to branch out (I'll assume you do as an HN member), and moving up to senior cannot hurt either.
Best of luck to you.
Yes - moving to Mountain View was one of the best decisions I ever made.