So, a while back (a year? a couple of years? not sure), I got all my contacts into Google, and have them shared among all the computers I use, and my phone as well. I did the same thing for calendars and to-do lists, but used something other than Google for that.
Things tend to get rather gunked up - email address included with no names attached, multiple instances of the same person (e.g., Chinese names in both last-first and first-last format), various spelling differences (women's pre- and post-married names), etc. So I spend some time going through the list and cleaning it up, consolidating, etc.
I am not sure whether I should be surprised by the large number of people listed whom I do not recognise. They're there, I must have had some communication with them at some point, and yet I have no idea who they are. If they have a corporate email address, that might help me recognise them, but if they have yahoo or gmail, it's pretty much hopeless.
I think I'll just let them go, rather than sending them all emails saying, "Please remind me who you are."