Snopes.com is about as useful as Wikipedia. Dig around there and see how often a negative opinion about a liberal politician is shown as “False”. Truthorfiction.com seems to be a little more unbiased.
Generally I agree. Snopes and Fact check can be wrong at times (particularly about conservative things). This time they weren't. The letter was written by a real person, Dewey Whetsell, and they pointed out he had his own blog as well.
As to the truth of the facts stated in the letter, a prior poster noted that the 11 AP fact checkers (I await any fact checking on Obama from these turkeys) didn't contradict Dewey's points, a good reason to believe the letter's content is true as well.