Step by step, Google Reader keeps growing and evolving.. recently I noticed a small but useful improvement, in the "mark read" section.
Namely, it's now possible not only "mark all read", but also to mark as read all the feeds older that one day, one week or two week. Very useful if you have a lot of feeds and you're away from your computer for a while. In this case, you probably cannot check all the updated feeds, but choose to check only the most recents.. once again, well done Google ! ;-)