OK, I'm more or less retiring nnrss in Gnus. The main problem is that more and more sites don't publish their full content in their RSS feed anymore, hence I have to read it via emacs-w3m anyway. So I figured, why not completely switch to nnshimbun ? Because it's tedious to write a shimbun for every feed, of course (see here and here for details on shimbuns in emacs-w3m). But since almost all sites I'm reading publish RSS feeds, albeit mostly without content or at least only with teasers, why not use a general RSS shimbun which simply inherits from sb-rss.el? So I wrote just that (there is already something like that in emacs-w3m, called rss-hash, but it's for feeds with fully published content).
This way, you can read every RSS feed with nnshimbun; it will ignore the content and fetch the HTML page for you, and you can easily extract the actual content by specifying regular expressions where it starts and ends. It gets even better: I added a detection for some popular blogging engines, namely Google's Blogger/Blogspot, WordPress and TypePad, and the shimbun will try to automatically extract the content for you if it encounters one of those.
The shimbun is called rss-blogs, although it works with practically any feed. To use it, get emacs-w3m from CVS and set the variable shimbun-rss-blogs-group-url-regexp, for example:

(setq shimbun-rss-blogs-group-url-regexp
  '(("Example: Wordpress" "http://emacs.wordpress.com/feed/")
    ("Example: w3m"
     "http://sourceforge.net/export/rss2_projnews.php?group_id=39518"
     "<a name=\"content\">" "<h3 class=\"titlebar\">")
    ("Example: w3m without removal"
     "http://sourceforge.net/export/rss2_projnews.php?group_id=39518"
     'none)))

In a nutshell: The name, the URL of the RSS feed, and optional two regexps for start and end of the actual content. If you omit the regexps, the auto-detection of Blogger/WordPress/TypePad will kick in. If you just use 'none, no filtering will be done whatsoever. See also the doc-string of the variable.
After you've set the variable, call gnus-group-make-shimbun-group, choose rss-blogs and then the name you've specified in the above variable.