I love Memento, my girlfriend took me to see it one night after she had already seen it the previous night because she was so bothered by many unanswered questions she had. It was a very innovative approach to telling the story, and was very orignal, however, unlike the Usual Suspects, which ties up just about every minute detail by the end, Memento doesn't do that.
Someone had posted all of the events in Memento in chronological order to some newsgroup, unfortunately, I no longer have a copy of it, but there are just a few too many unanswered questions in the movie for me to even bother giving it much thought, it is not one of the great movies that have been made, although I think it could have been if it were well written.
They took an incredible new idea and just didn't deliver like they could have. I realize you are supposed to walk away from that movie with a few unanswered questions in your mind, lots of movies leave you hanging like that, but if you examine the list of events in chronological order, there are a few too many unanswered questions almost to the point of being mistakes, I'll look for that essay, if someone else has a copy, please post it or at least a link to it, thanks in advance.
Don't get me wrong, Memento is well worth seeing, and I recomend it to everyone after they tell me they have never heard of it, but it isn't really worth watching more than 2 or 3 times.