How far is too far when growing your network through online friends, connections and followers?

Last Thursday morning I went to an intimate vendor presentation attended by me and two other companies.  I was there early enough to enjoy the bagels and drinks and meet the other two women attending and exchange business cards with them.  At the time they both appeared as new people in my life.During the presentation I looked more closely at one woman and she started to look familiar to me.  So I looked at her business card and her name was familiar to me this time.  So I tuned out for the next 5 minutes to go on an obsession binge of mine.  Whipping out my Blackberry Storm I pulled up my LinkedIn profile to see if we shared a connection.Oh Crap!We were connected on LinkedIn!  We didn't share a common acquaintance.  We were first degree connections.  How could I not know her?I am not one of the people obsessed with growing my LinkedIn database with random invite requests.  Every invite request I've sent out or accepted has been the result of an actual in-person meeting or a 1-to-1 email exchange.  A type of interaction where I would not be ashamed to ask for a LinkedIn connection.So what was broken here?  Some of my guesses:

1. My memory: That's not an unlikely reason for me not recognizing her.  I'm not the best at remembering people.  But here's the kicker on that one.  I found her in my Outlook Contacts.  Not the main one we all keep up-to-date, but rather Outlook's "Collected Contacts" database that gets created on the fly from all of your emails sent or received.  A quick look at the date it was created found April of 2009.  Less than a year ago!  Again, what is going wrong with my memory that I have had a interaction with someone less than a year ago not not know from where?
2. Two of my worlds have collided: Maybe I met her socially and decided to link with her.  It's rare that I do that, but I do think differently socially than I do professionally so maybe that's why I don't remember her.  I also meet a lot more people outside of work than I do at work so I could then blame it again on #1 above, my memory.
3. I don't know here well enough to be LinkedIn: I'm beginning to think that must be the answer.  Given the email exchange (which I could not find) I guess I went out there any linked in to her.  Not proud of that.  That is not what I want to be known for or to use LinkedIn for.  It devalues it and the relationships I have with those already on LinkedIn.

So what's the moral here?

First I'm going to reach out to that woman and have an email exchange so that I can justify having her in my list of connections.  But more important than that I'm going to be more diligent in growing and cataloging my relationships in the various social networks.Twitter is a different beast and serves a different role regarding followers and the implied relationship we have with them.  Facebook is yet another that has grown from a high school reunion into a "your life as a cocktail party".  But if LinkedIn is truly "your resume" as quoted by Brent Britton then you really need to know everyone there.And finally if you're reading this and we're connected on LinkedIn when we shouldn't be, feel free to un-link me.  I'll send a request when I deserve it.