If bandwidth is a concern (and when is it not?) and you’re already supporting conditional GET, the next step is to support gzip compression. I’ve mentioned this before (1, 2, 3, 4). There are a number of tutorials on it, and all modern browsers support it. It can compress HTML markup by 85%. It works great on syndicated feeds, too. My (not-)Echo prototype? 29K. Compressed? 9K. Of course you’ll only see these savings with a news aggregator that supports compression, but a growing number do (updated link, thanks Dare), including my ultra-liberal feed parser.

