[cema]

Boston area tends to have relatively low salaries, both compared to competing areas (like the Silicon Valley, NYC, and Washington-Baltimore corridor) and relative to the cost of living (real estate, primarily). The difference is not trivial.

[m0nastic]

My experiences haven't found it to be that cut-and-dry:

I moved from Boston to Silicon Valley in '99, and found it was significantly more expensive with only marginally better salary (which I was happy to accept as we would leave at lunch and go surfing, which for me was a worthwhile tradeoff).

I moved from SV to Washington DC in '01, and found the cost of living slightly less, but salaries approximately the same.

I'm now in the process of moving to NYC, and the cost of living and salaries both are a little higher (I don't really care about money though, so I'll admit that it hasn't been a factor in my moving decision).