Ok, I log in as user1. my id is 123.
Once I login, you use a classic session variable to hold:
session("userID"

= 123
Then, I view article1, and tell you I'd like to save it. At that point, you make an entry into table, tblArticles, and it would looke like this:
userID | articleID
--------------------
123 | 1
Unless I'm missing your point completely, that should wholely solve the problem. At that point, if I go and log back into another application, then my userID is still 123, right? So you go grab:
SELECT articleID FROM tblArticles WHERE userID = 123;
And typically, I'll have a nice handful of them in there.
If you're trying to uniquely identify a user w/o the use of a customized id, i.e. one that I would sign up for, then I don't see how you could do that. The only way would be like I've described.
Am I missing something, or is that what you need?

paul