Is this "I" in the figurative/coding sense, e.g. "how can I create a script that says who's in which forum/page like here at PHPBuilder?", or "I" in the actual sense, like, "I want to view and meddle in all the activities of my puny little users, MUWAHAHAHAA..." ?? 😃
It probably doesn't matter, really. The DB is your best shot. Any kind of storage is going to the server filesystem anyway, so you might as well use the built in mechanisms as to spend time writing your own. Most SQL servers are built to handle a lot of transactions, so unless we're talking about a really high trafficked site, it's probably not going to affect things too much. <#include disclaimer.h>
My $0.02,