I personally know quite a few people who met on sl and are now married with children in rl. I myself met my rl fiance on a dating site and we have a son it can work but you have to be willing to go the distance!
My rl hubby and i both play sl and talking about it mutually in rl we agreed that its okay to have a relationship in sl if it STAYS STRICTLY sl nothing outside of. It iis all based on trust and knowing that you will never split in rl over a sl relationship. I say make sure its okay with the person you are with in rl before jumping into anything in sl.