Lets be honest here. Go up to Mass...and look for new folks moving in. First, you won't find more than 100 southerners who have packed up and moved into Mass...it just doesn't happen unless you got desperate to marry some gal or dude from the state. Folks from the left coast moving to Mass...hardly ever..same way for midwest folks. You might find two or three thousand folks from Penn, NY or Maryland moving in...just to be with relatives or because of the job.
But now, with moving out...I'd bet the south is gaining most of those moving out. Retirees are finding Florida to much cheaper, and much better weather than Mass. Why stay in your older years?
So my prediction. 2010 will spell the end of one seat in congress for Mass. So they will go from 10 down to 9. I also will predict the population trend to continue through 2020, and at least another seat (maybe even two seats), will go by 2020. So you may live to see the state with just seven Representatives, and a bit less strength in the electoral college.