On May 17th, 2009, at 10:37 A.M., fire alarms began sounding during a regional stake conference at the Longfellow Park LDS chapel in Cambridge, Massachusetts. The estimated 500 congregants (according to the Boston Herald) quickly evacuated while the flames rapidly spread. Around 20 minutes later, the roof began to collapse, and despite a timely and efficient response from 80 firefighters in fire departments from nearby Belmont, Somerville, Waltham, and Watertown, the building was a total loss, although the steeple did not collapse. A current story is also available from the Boston Globe and on the Mormon Times.
Here's a YouTube video which shows more dramatic (and depressing) footage. You can see how one side of the chapel has become fully involved:
Arson is not suspected at this time. No threats against LDS facilities in the area have been noted. The fire is believed to have originated in the attic, and there is informed speculation that an electrical short triggered the fire, which may have smouldered in the attic for an extended period before breaking loose.
A series of 200 photos can also be viewed on this Picasaweb account.
Additional unofficial LDS reaction is posted on Mormonism Unveiled, the Faith Promoting Rumor blog, By Common Consent, and My Imaginary Blog.