I'm a new Google Reader convert, and I'm experiencing a problem that I can put down only to the fact that The Old Reader is taking considerable time to find and catch up with my feeds.

I had manually marked as read all of the many thousands of posts that were more than about two weeks old. However, over the next couple of days, I keep noticing new items appearing in my list that are more than two weeks old (and others that are less than two weeks as well, although it's hard to tell which of these are new additions and which I'd already seen, since they appear mid-list.)

It seems that your list sorts based on the date tag in the RSS feed for a given item. To me, the date flagged on the feed is much less important than the date on which The Old Reader discovered the item, and I'd like to see the ability to sort based on the discovery date instead.

That would prevent me missing what are, to me (and The Old Reader) essentially new posts, but which currently first appear well down the list between posts I've already seen.