My workplace is very queer-friendly, but sometimes it's hard being the Rainbow Ambassador. Neither my sapphic team mate or I could come up with an answer. We googled the various combinations of letters until we found that "I" stands for "intersexed". "Q" could actually be for "questioning" as well as queer and "A" could be for either "allies" or "asexual".
I'm still a little vague on how asexual is different from "can't get laid", and why asexuals feel the need for inclusion when they've sworn off sex in the first place.
If this trend continues, pretty soon we'll be able to simply use the word "everyone".
I think Big Bird sums it up nicely in his/her/its classic song from Sesame Street, with the line, "It starts out like an 'A' word, as anyone can see. But somewhere in the middle, it sounds awfully queer to me."