jowilson

Well, I don’t know everything about your configuration. Maybe you’re not using the same webserver I am, and when PHP sends out the 304 error, your server helpfully stops any more output from being sent to the browser at that point.
When I looked at my logs, over the past two weeks, I was sending out approximately 20k per RSS request, whether my feed had changed or not. When I grouped and sorted by response code, it came out to a total of 40 megs of wasted bandwidth, not very much, but I only have about 10 subscribers to my RSS feed. It comes out to about 8 megs per subscriber per month, on average.
I’ve since enabled gzip encoding of feeds; that ought to shrink them down a bit.

Maybe you’re not understanding what I mean.
Wordpress sends the 304: Not Modified header just like it’s supposed to. Then it appends the full text of the feed because it doesn’t halt the script at that point.
If you don’t believe me, telnet into your server on port 80, and paste this in:
GET /path_to_your_weblog/wp-rss2.php HTTP/1.1
Host: www.yourhosthere.com
If-Modified-Since: Mon, 20 Dec 2004 19:05:13 GMT
Connection: close
Hit enter twice; watch and be amazed as all the pretty text flies up your screen. You may have to fix the date, depending on when you last updated your weblog, of course.