Look while I always prefer a number, sometimes it can be helpful logistically to close/exchange info through facebook. edit: I find this is most helpful for social circle game. If you have pretty strong privacy settings, it can be hard for people to find you. Make sure you have an easily rememberable facebook.com url

Set it here:

http://www.facebook.com/username/

I find that this can be useful to drop in conversations where facebook comes up naturally, or maybe you take a group picture and tell your target to add you if wants to be tagged, she is in the middle of her social circle and would feel uncomfortable giving a number in font of her peers, etc. Also helpful for sets that are quickly moving venues but you established quick attraction and feel a number would be flakly. I basically use it as a sly contact exchange. (Would you rather have a way to contact her, or no way at all?) I've gotten plenty of girls to find and add me just by dropping my simple url into a conversation. This also can work to find out which girl in the group of girls is possibly interested in you, if you share this info organically to the whole group (shy cute girls love to fbook add). Also, some girls might be flaky over text message, but will easily let you build attraction over facebook (comments on your status updates, responds to wall posts, receptive to facebook chat)