I wanted to have an RSS feed be returned, for a specific tag or search item in WordPress. Hopping on to IRC, and speaking with Dossy, we realised that there was no plugin to do this. However, after a short amount of poking around (circa under 2 minutes?), the way was clear:
?feed=rss2&s=STRING
Now I can have a specific lca08 feed. Or one for the eeepc. And the list can go on…
FWIW, feed= can be rss, atom; basically anything WordPress supports.