Overload!!! - How to keep the important contacts viable

Networking, Meeting, After-Hour socials, etc. etc. etc.  We meet so many people and these days it seems like EVERYTHING we do (work related anyway) has to do with meeting new/different folks and getting our company in front of potential clients.  But is this really the right thing to do?

I've always been a big fan of 'guerrilla marketing' in that, I've got a good group of folks we work on a regular basis, and all us (small firms) collectively look for new gigs.  Because I've been doing this a while, my firm name is circulating around I'm getting invited to new groups/organizations.  It seems like a good number of these new folks ('contacts') are people I want to/should or need to keep in contact with; I hate email only (too impersonal), Phone calls are in intrusion, (unless of course someone says 'call me'), so what's the best way to stay in contact?

Bigger question- what's the best way to remind myself 'when' is the time I should stay in contact? How is the best way to remind myself or my team that 'hey, we need to talk to the guy blablabla".

Just wondering... for now, I'll stick with putting business cards in a index card box divided with monthly tabs - next month, I flip to that tab, pull out the business cards, flip through them and decide if I should call or click...How do you guys do it?