Haven't ever moved in with a girl. We just never got to that point.
Someone once mentioned to me this study/statistic that said that engaged couples that lived together before marriage split up more than couples who moved in together after marriage.
I never did read the piece to be able to call BS on it. But I think the logic behind it was (as my friend explained it), when they lived together before being married, they were more open to breaking it off if living together proved difficult. It seemed that being married forced more couples to try and work through differences.
Again, I couldn't speak to how true that might be.
On some level, it just seems logical to live together before being married...just to see if you're compatible with all the quirks your partner has that don't show up when you live apart.