A strong network is a critical tool in managing your career because more positions and assignments are found through a network than any other way.Find more here
However unique the meeting, you will not remember the person after a few weeks. Organize your contacts into categories in a database. Note where and when you met the person. Input the data ASAP.
Try to keep in touch with an occasional call or email. Doing this builds relationships and a sense of history between parties.
Keep in mind that a network is a two-way street. Do not call people only if you need something. You will be seen as a user.
I use my network to make introductions between people whom I believe should know each other, and it has proven to be a great tool in creating other relationships. I would always rather do a favor than ask for one. It is better for relationships, and provides a lot of chips to call in if ever you need some help.
My Comment: the main thing a recruiter can offer someone is a job. And, that's not something you just have hanging around to give when someone calls for a favour. So, I think it can be hard to make the relationship reciprocal.