One of the strengths of blogs is that the freshest content is at the top of the page. Indeed, it was this design convention above all others, that led to the blog explosion. I remember having conversations with other people who published zines and personal soap boxes circa 1998 about the importance of updating content at least once a week. Otherwise people wouldn't check back to the site. The other thing we did in those days was send an email announcement when we'd updated our sites, back before our inboxes were what they are now.
I was having a conversation with Bob Baxley the other day about the importance of surfacing aging content. A lot of really great content on blogs tends to languish unread once it's dropped off the front page. One of the things that happens with Flickr is that I notice when visiting my "new comments" page is that people are commenting on photos, adding them to their favorites, and viewing photos that are often more than a year old. And the reason for this is that people are finding the photos in ways other than my chronological photostream: they are finding them through tag searches, or when browsing group pools.
There are a bunch of blogs out there that append a list of their categories on the sidebar, like Common Craft, which I visited today. Tech Ronin not only links the categories on the side, she links them under each post, as well as tagging them and linking back to the Technorati tag page (and let me take this moment to congratulate Technorati on their new launch!). I'd be willing to bet the content on blogs with such link practices stays alive in ways that the content of mine do not. As blogs enter their teenage years, and many people have 6-7 years of posts, surfacing this stuff will be more important.
I'm also thinking a great thing to build would be a flexible blog post microformat that can delaminate blogs from their native domains and aggregate all posts by tag or category in an RSS reader.