This blurb from the microsummaries page at Firefox is interesting:
Microsummaries are regularly-updated succinct summaries of web pages. They are compact enough to fit in the space available to a bookmark label, provide more useful information about pages than static page titles, and are regularly updated as new information becomes available.
Microsummaries are better than page titles at labeling bookmarks because they give users quicker access to the most interesting information behind a bookmark and provide sites with a way to notify users of updates and entice them to revisit the site.
As with a large number of recent web features, microsummaries rely on a link in the HTML header content:
<link rel="microsummary" type="application/x.microsummary+xml" href="/index-microsummary.xml">
While Firefox is interested in using this concept for “dynamic” bookmarks, there’s also a lot one could make of it for portals and the like. If other pages (on other servers, even) can tell you a nice summary of itself, constructing portals can become really easy.