The last Sabine's Gull reported in Massachusetts this year was on October 12th, three days before our trip!
Interestingly, however, another one was apparently just reported Nov 8th on the Maine/Canadian border....
Sabine's Gull, November 8, 2011 - Chris - Picasa Web Albums
So there may still be a few in the US northeast this year, along the coast, and out on the ocean.