I got trolled on an online game not so long ago. I was surprised that although they managed to follow me as far as, I think, fanfiction.net, they never got any further. Leastways, there was never a pip out of them on LJ and they were, briefly, determined to cause maximum heart-ache. I suspect, mind you, I was protected more by their stupidity than because my LJ identity is particularly difficult to ascertain.

But, as you say, if its going to be a catastrophe if someone discovers something about you, then don't reveal it online, especially in any social networking space. Or, if you do, be careful enough about your anonymity that the linkage of a couple of data bases won't bring the whole thing crashing down.