Well, it is as big an issue with us as it is with the Presbyterians and Methodists, to name a couple. Little wonder: the various denominational groups (e.g., "Integrity" for the ECUSA, "Dignity" for Catholics, and so on) operate under what appears to be a common umbrella political organization.
The Episcopal church is perhaps more prone to "take-over" by such groups because the bishop is quite powerful, and the fact that the selection of bishops is easily politicized. Once the gay (or whatever) groups can get one of "theirs" in, then it's well-nigh impossible to get him out.
We traditionalists have tended to ignore the political aspects of the matter, which explains why we're losing ground at the political level, and I have to say that it's the right approach even if it does cause short-term loss. (However, the healthiest parishes are mostly traditional, so eventually the problem may become self-correcting.)