Here are three articles with some info, at least one of the FR links (and maybe both) have more info down the thread as well. Scripter is the man when it comes to knowing all, I haven't seen him lately as he is very busy. Maybe he'll notice this and toss something our way!
How Might Homosexuality Develop?
Putting the Pieces Together
Root Causes, Homosexual Consequences
You are right, a large majority of homosexuals were molested when either pre-pubescent children or young adolescents.
The Root Causes, Homosexual Consequences (People can Change) link has a reference to their own study. The study, a PDF document is very interesting, especially pages 6-9 which hit on the abuse factors. That is, (page 8) ~48% claim to have been sexually abused.