Transits of Mercury are more frequent and less exciting than Transits of Venus, so Nomi and I have no plans to observe this one live, as we did for the Transit of Venus back on June 8, 2004. (And anyway, the weather prediction for Massachusetts tomorrow is for clouds and rain.) But for those of you in our hemisphere who wish to observe it, the Transit should be visible from much of the United States. It begins at 2:12 pm EST (7:12 pm GMT) and ends close to 7:08 pm EST (12:08 am GMT Thursday). That means those of you in the Pacific Northwest will actually be able to observe the whole Transit, from beginning to end; those of us in the East Coast will see the sun set before the Transit is complete.
For more information and some nice graphics, Sky & Telescope's website has a great article: Mercury's Day in the Sun.