I was 15 minutes slower than what I had wanted, but my training hadn't been the best and it was my first Boston. Wow that course is hard.
Personally, I felt running with a crowd of people (I ran 3:10) with a tailwind made it feel too hot for me. There were no clouds. I was happy to get a breeze when we did and running closer to Boston and when crowds thinned and the roads opened up it felt much cooler. If you are ready and ready for the course, it could have been really fast, but if you can't handle all that downhill, the tailwind is only going to make you run faster, which is only going to trash your legs faster. Still, Boston is always Boston and I hope to return next in better condition, even if with less-than-perfect conditions.