i dated a girl i met in l2 for 2.5 years. 2 friends of mine complete 5 years last month and met ingame too.
i think that dating someone you met in a game is like overenchanting, it always ends up breaking up :d
it works depends how serious people are takin such relationship (my previous cpl from long time merried to our archer when she was in poland and he was in italy(he was polish too but living in italy) he fight all way to poland to be togther with her