I've been on online dating sites before and I do notice some things you should note:
1) Some women delete your message without even reading it. They basically look at your picture -- make an immediate assessment --- then hit the delete key. Some do not even bother to look at your profile either. They are also so busy with others bothering them online they have to make that split second decision.
2) If you get some to MSN chat with you -- chances are she is simultaneously chatting with a few other guys as well.
3) Like the other poster said -- you can't do BT spikes, DHV live, do BL, banter etc. You are better off (in some cases just doing straight bar pick up). Examples: I have had cases where I sent smiles and/or messages to girls online but got nothing back in return. My city is small compared to something like LA so chances are you can/do meet these women in "singles" events/bars, etc... and I'm pretty sure they do not remember me (or at least have never brought it up). I did the normal pick up stuff and got them hooked --- but then just for a bit of revenge --- I punted them out when they tried closing on me:)
4) Also --- when women enter in their search criteria, race, age, height ect -- you probably will not show up in the search results. You might get better results just to log in and just forgte about it --- that way you show up as being "online" and they can message you if they search for users online now in my city -- and you can capture some interest.
