It seems just as obvious as when your mother said: even if a man offers you candy, don't get into his car. But emailing with someone can create a false sense of familiarity, and therefore, security. "Meeting someone online these days I think is safer than meeting someone offline. You have a chance to learn about the person before you meet," says Jim Safka, CEO of Match.com, which is now in 33 countries and 18 different languages. Still, Safka recommends "meeting at Starbucks for 15 minutes."
I'm no CEO of a dating site, but I'd recommend blocking off an hour, and mentioning even before the date that you have plans later on. That's your escape chute. If you're enjoying yourself, then those "plans" can always be changed or delayed.
And let a friend know where you're going. Just like you would have told dear old Mom.