If you're planning to attend Macworld Expo in Boston (the show runs from July 12 - 15) and you haven't made a room reservation, do so ASAP.
Accommodations close to the convention center, such as the Seaport Hotel, are completely booked up. Less expensive hotels such as the DoubleTree Club Boston Bayside are sold out as well. If you're looking for a discount, try the Macworld Expo Hotel and Travel page for information on properties willing to give Expo attendees a deal.
If you can't find anything close to the convention center, look for lodgings near Boston's T subway system. The new Silver Line drops you off at the convention center and the Green Line gets you darned close.
You can find a subway map in PDF format here.