This is not personal experience per se, but my family is Jewish and I have many Jewish friends. One friend, who's actually studying Hebrew in college, had one of the warmest reactions imaginable when I told him about my girlfriend. 'Course, he's gay himself, but hey.
I have a feeling that my family would be okay with it. Some of them might not 'understand,' and some might be 'confused,' but I don't think any of them would go so far as to disown a transperson or treat them badly. I think the worst reaction would be awkwardness once in a while or a barrage of questions. But there'd be some 'best' reactions, too.
A mixed bag I guess. Lots of generations and varying levels of 'liberalness' in my family.