Join Date: Jan 2006
Location: New England
Programs: American Airlines, Continental, United, Southwest, BA, Marriott Rewards, Hilton Honors, Hyatt
Posts: 272
They won't close any roads from Woods Hole to South Station since it is across the city from where the marathon takes place. It is easy from South Station to take the Silver Line to the airport or it is a short cab ride.
The Marathon takes place on Patriot's Day which is also the start of April school vacation in Massachusetts, so it can be pretty crowded and the hotels are sold out early and the prices are expensive. You should see if you conference hotel will allow you to extend your dates pre and post if you decide to stay in Boston.
Weather in April can run the gamut from sunny and in the 60's or 70's or it can be cold with rain and snow showers. Martha's Vineyard will be quiet since it is more of the off season, but you will be limited in getting around if you don't have a car. I would stay in Boston if I had the choice because there is just so much to do and see .
Regardless of what you decide, have fun!