After having built the system on our new CMS, and a couple suggestions from a friend, I came up with a better tracking system as I originally detailed on my blog. The new system is combination of the second method detailed in the post, and a much more accurate solution.

We continue to track the last login time in our session (and database, if they’re logged in), but we now also track a time for each object they have viewed. Whenever they view an object, you update a list in your session w/ that object’s key, and the current time. Now you simply compare the time they viewed that object (if it exists) with the last updated time, and you have a quick, database-free, tracking solution.