As a backend engineer, one of my favorite features of Google Reader is its ability to track the history of a feed over time. Reader takes a snapshot of feeds periodically and saves the content, so you can see posts that are days or weeks old. It's a neat way to read the web; in a way, it lets you look back in time. Combined with Reader's ability to track what you have and haven't read, you can safely jet off to Tahiti for a few weeks and never miss a post.
Ideally, though, you'd like to catch up on those posts in the order they were written. That's why we're releasing one of our most requested features: sorting by oldest-first. Now you can read those Lost episode summaries in the right order after you've shook the sand out of your shoes. It's available in the view settings menu, so you can select it only for the feeds or folders you prefer.
Careful observers will note that we've also added sort by auto to view settings. This nifty feature mixes feeds together according to posting frequency, so items from rarely-updated feeds (your friend's blog) show up higher than items from frequently-updated feeds like The New York Times. Look for this feature to evolve over time as we try to find other ways of highlighting the most interesting content in your feeds. Enjoy!