After living and working in Boston since June, here's my take, in the form of completely random thoughts:

- It's generally hot as balls in summer and has already gotten quite cold. Neither of these particularly bother me, assuming A/Cs and heaters are available.

- It's cheap as hell to live here, as long as you live slightly off the beaten path. We're currently living in Medford, a 15 minute walk from Davis square and we pay about $1,400 (or was it $1,200?) a month for an apartment with 3 bedrooms (only two people, but we are gluttons for open space), an "office" (no idea the technical term of this room), living room, kitchen, etc. The building is old as shit and it would cost a small fortune to heat conventionally (hello 1920s oil heating!), but... it's damn cheap.

- The start-up scene is a bit lacking, but there are lots of people here if you look. I probably can't walk into any random Starbucks and run into an entrepreneur, but we're here. We even have a poker night!

- I don't think the pond analogy has any relevance here. With the proliferation of the Internet and a global economy, I'm not convinced it matters where you're located for the most part, especially if you're doing a web start-up. Yes, there are lots more investors in SV, but there are investors here, too -- ones who don't see 900 pitches a day. The investors here all talk about how they want to make Boston investing relevant again.

- And they're proactive about it. They regularly host firm-sponsored events and invite a bunch of interesting companies. We've been to a small dinner party and have a cocktail party coming up. We were even taken out Paintballing by Battery Ventures (Adam Marcus is a great guy, btw) -- that was a profitable day; we got to keep the Battery-stamped masks they provided and ended up taking home 3 cases of beer. We met some interesting companies too, but I was mostly busy shooting VCs.

- Boston as a city is fun and there is certainly a lot to do on the rare occasions we go out. I sure as hell miss all my entrepreneur friends who moved to SF (traitors!), but Dan and I are kept busy enough by the business that I might notice the lessened night-life/culture more if I had more free time.

All that being said, the Pros you supplied for SV are definitely true. We plan to move to SF (Mountain View is pretty dull in my experience, but SF is a great time) when we have more revenue (we did the math; it's a lot cheaper here), but for now I don't really feel like we're handicapped by our location and we're definitely better off than we'd be somewhere like the black hole I come from (Ohio; just threw up in my mouth a little).

I can't speak for your company, but as a business with very low costs and the advantage of not having to immediately and aggressively seek out investment, Boston is the perfect place for us right now. The low cost of living allowed us to become profitable the first month we operated and this type of city allows us to take part in a very diverse (though comparatively sparse) start-up community while supplying plenty of entertainment and cheap/convenient transportation to get to it.

Edit: I should point out that personal preference / taste matters here, too. You might be able to live for a comparable price in SV/SF if, unlike Dan and I, you do not become instantly claustrophobic when supplied with less than twice the amount of space most people seem OK with.

Finally, unless you already have an excessive number of possessions (like a family), moving isn't that serious of a deal and you might find in either location that after 6 months you want to try the other.