I just though my 2 cents needs to be put in here~
I think it can be bad, because you just have to imagine if you're a gay guy, and an AMAZING crossplaying girl starts flirting with you, you exchange phone numbers, and it turns out it's a chick.
That, would just be uncomfortable.
Then again, I actually hung with my girlfriend at a con for the first time, so I'd say that you could so do it if you wanted to xD
(Can you say "bump"? xD)