You know how I'm always harping on the need to minimize bandwidth consumption by feed readers? Here's an idea that could help: automatic refresh interval adjustment. Some feeds are updated daily. Some are updated every few minutes. Some are updated every few months. Those that are updated infrequently don't need to be refreshed as often, but my gut tells me that few subscribers ever adjust their refresh interval. Digest readers ought to be able to adjust their refresh intervals to match automatically without too much trouble.

Brainstorming on how it might work: When you subscribe, you set initial, minimum and maximum refresh intervals (reasonable defaults should be supplied, of course). Then the software takes over, keeping track of the minimum, maximum, average, standard deviation, whatever, amount of time between entries being added to the feed. It could keep track of recent data separate from all-time or long-time data to allow it to adjust to changing update frequencies reasonably quickly. It could track related data like days of the week and times of day that rarely see new entries (a feed that's updated hourly during weekday work hours but never during nights or weekends would average an update every 4.2 hours if such things weren't taken into account).

Once it's got some data, it runs it through some fancy formula and adjusts how often it checks for updates. If, on a feed where the interval is long, it checks in around the time it expects an update and doesn't get one, it can switch into a more frequent checking mode till it does get one.

A nice related feature would be alerts of stale feeds--those which haven't been updated for some number of days. No point wasting bandwidth on feeds that aren't being maintained.