Your question is a big part of the reason that I tend to seek and destroy auto-update processes, and prefer to rely on performing a periodic check for updates myself. I'm capable of running updates once a week or more, without using up RAM forever and ever. :)
So, having said that, one method you might use for nailing down the culprit would be to determine which apps you have installed that are performing background updates (Firefox, iTunes, Notepad++, uTorrent, Google Update, Real Player, Java, etc) and try to use their manual "check for updates" facility and see which of them fails to complete successfully.
However, if you believe that the problem is specific to the actual background update process you might track it down by disabling them one at a time until the problem disappears. I use WinPatrol, but the "msconfig" utility (Start | Run | msconfig) will also allow you to disable those processes. (And more, so use it wisely.)
Several people offered very good suggestions, but ultimately "netstat -b" plus looking for 'ESTABLISHED' was the "most correct" answer for me! Thanks all! – Brian Knoblauch – 2009-10-03T01:45:27.713