I read Yaoi/Shounen-ai, but it sorta ends with effeminate boys. (Muscle men are intimidating, outside "Inukami".) I consider myself fairly straight (with as much certainty as anyone can truly have).
And while I greatly love the female form, I've yet to read any work of Yuri, whose quality could compare to "Loveless"... (With exception to "Girl Friends", but I don't think one series can carry an entire genre). Yaoi has more substance, based in reality, than Yuri, for me, from most works. I find it easier to enjoy the story because there is a story being told.
The goal of reading both, for me, is to read a story of "striving for forbidden and prosecuted love", "to form a basis of normality, in their world, with something socially unacceptable", but (male orientated) Yuri/Shoujo-ai is, more or less, objectified (imo, for extra measure). I can't enjoy most that passes for Yuri/Shoujo-ai. So I turn to Yaoi for deeper stories.
They're a few "Jousei" series I've read here and there, etched into the furthest reaches of my memory, that I thought portrayed or borderline'd the subjects matter of Yuri/Shoujo-ai rather well... Just can't seem to remember any of them... I usual separate my opinion of those from the male directed material.
Also(edit): To those making statements, that, "in order to enjoy Homosexual stories you have to have homosexual tendencies", can't I reverse that back to say, "gay and lesbian couples who participate in watching straight material have heterosexual tendencies"?
Or, simply, "the absence of heterosexual tendencies means homosexuals can not enjoy hetero stories/subject matters". Which sounds like a rather weird statement.
And that, in order to enjoy any material with a subject matter, you have to have tendencies associated with the subject matter. I find that highly debatable. For an easy example, how would this equate that to math, science, history, philosophy, ect?
I believe everyone (who states you have to be gay to enjoy Yaoi) is misappropriating Social Views with Sexual Orientation.