My husband started doing this on the advice of a lady we work with. I guess the catch is, as someone else stated, that you can't guarantee the bees will have pollen for what you are allergic to, and that that may change over time (so if you're allergic to summer plants, you may have to get spring/summer honey, which kind of sucks, because you have to wait).

For both of them, a teaspoon definitely caused the sniffles and an allergic response. Slowly eating the honey every day, and increasing to 2 teaspoons a day, made their tolerance to the same honey less severe. It also increased my husband's tolerance to beer made with semi-local (regionally local anyway) hops. The lady I work with says it definitely made a difference to her allergies, but had to start out small.

So, as with all things, it seems to be a YMMV