I live in the Southern US, and I have a lot to say on this. However I'm on my phone, so bear with me!
Inside of supposed LGBT spaces, I've experienced a great deal of transphobia, mostly from gay men. They seem to think I'm a self-hating homophobic gay man even though I'm in a long term relationship with a woman. They continually call me "->-bleeped-<-" "->-bleeped-<-" and "that confused dude who thinks he's a woman". I asked, politely for awhile, to not have those terms used and for the blatant misgendering to stop. No such luck there, but they sure expect me to show up at the state house for marriage equality protests... to hell with 'em.
Online my experience has been almost as bad. I don't like LGBT groups, they really mean LG...b. T isn't even an afterthought most if the time.
While I think there is immense value in alliance, as we have historically had similar experiences (facing familial loss for coming out, job loss, discrimination, etc) the attitudes have changed in the past 2 decades to where LGBs have a majority of mainstream support. Homophobia sees the same level of disapproval as racism did in the 80s, so in another 5-10 years they'll just be a regular part of society. Activism for them is a lot different than it is for us... while we still largely face discrimination in the workplace, they only have minimal problems with the issue. Violence against them is seen as an actual crime - violence against us is still riddled with transpanic defenses which on the whole are still successful. We cannot expect their help, though I regularly try to take them to task for their hypocrisy.