I know many people who move in immediately. Lately that seems to be in style, at least in my area it is. For some reason, there's a lot of pressure on a woman (and men, but speaking from my own experience) to move out with a partner immediately and have children. It seems that women are looked down on if they take it slow, again that's speaking from my own recent experience. I was at my OB/GYN last month and was "lectured" by a nurse about still being at home and not moved out, with children. She didn't seem to care that I had a strong opinion and plan for my life and that until my partner and I finish school and get married, we don't plan to move out. She was very unhappy with my decision. I however, think that there is not set time for anybody to move out together. It's strictly up to the couple, when they are totally ready. I for one, want to finish school and start further into my career, and marry him before doing so. That is very unaccepted in my area at the moment. I also am only 21 years old! What is so wrong with just waiting?
I have seen a lot of bad results with couples who move out before knowing each other's last name. I've also seen couples move in together quickly and have an amazing relationship. I have responsibilities at home and cannot just up and leave children and a home whom I care for.
I would definitely say it needs to be thought through very carefully. It is a big decision. I also would not let others pressure you into it.