My group is likely not aware of it, and I am ambivalent towards it, anyway. When we celebrate the GM, it's usually on his/her birthday, and usually by a birthday present that they can use when gaming. On my birthday/christmas in 2001, my group pre-bought me the Call of Cthulhu d20 book, and Masters of the Wild. In 2002, they bought me a ton of fantasy novels that I could not only enjoy but plagarize for adventures; in 2003 they bought me the minis handbook which I still use a bit; and last year, since money was tight we all exchanged some small tokens, but in general some pretty cool stuff.
That reminds me - one of my GMs is having his birthday in a couple of months...