Okay, maybe using If-Modified-Since to throttle RSS bandwidth isn’t such a great idea. If I understand the objection correctly, the problem goes something like this:

1. Tom requests the feed, and the caching proxy retrieves items X and Y.
2. Dick requests the feed, and the caching proxy replaces items X and Y with Z.
3. Harry requests the feed, receives item Z from the cache and never sees X or Y.

It seems to me that using If-Modified-Since to throttle RSS bandwidth can still be effective by introducing a minimum number of items. My feed currently contains 25 items. If I introduced If-Modified-Since throttling with a minimum of 7 items, then I’d still get a substantial savings in bandwidth without unduly penalizing readers behind a cache proxy.

PS: This is of course contingent upon my rumored migration to TextPattern.

PPS: I am aware of RFC 3229 and I choose to ignore it. The problem isn’t with well-behaved, standards conforming aggregators.