It's conjectured. Of course, we will never really know for certain. It's entirely even possible that Socrates is a figment of Plato's imagination, as the only accounts of Socrates come from Plato.
His crime of "corrupting the youth" for which he was put to death was either from being heavily anti-war or being heavily pro-homosexual and encouraging of free love. As Michael Foucault pointed out, the reason that the Greeks talked frequently about homosexuality is because they were conflicted about homosexuality. They never talked about heterosexuality because in their minds, heterosexuality was (in their minds) self-evident: the man did manly things, and the woman stayed at home and raised the kids and darned the socks. Sort of like how prop 8 arguments periodically pop up in the politics forum. You never hear anything about racial segregation anymore, because our society has resolved that racial segregation is self-evidently a bad thing.
In the Symposium, one of Socrates' friends desires to sleep next to him (or possibly, engage in homosexual activities with him) because he believes it might impart some of Socrates's wisdom into him. Of course, it was just used as a springboard for Socrates defining what Wisdom truly is, but the fact that the companion (his name escapes me) was so flippant about cozying up with Socrates that Socrates may have swung that way.
Of course, he did have a wife, named Xanthippe, but Xanthippe was a woman of such legendary henpecking that Socrates preferred to hang out in the streets chatting with whoever would talk to him rather than go home. He was famous for the quote "My advice to you is to get married. If you marry a good woman, you will be happy for the rest of your life. If you don't you will become a philosopher". That he may have been homosexual may be reinforced by the fact that he had an unhappy marriage.
In any event, it's completely irrelevant to Socrates's place in history, and whether he was or wasn't has no bearing on his status as one of the great thinkers in western philosophy.