Nice. Here’s a useful Bing search modifier that Google doesn’t have…

feed:keyword

…finds only RSS feeds.

In Google you’d have to use this sort of roundabout method…

inurl:rss keyword

inurl:feed keyword

Or chain the two main types together with all the minor possibilities such as rdf…

inurl:rss OR inurl:feed OR inurl:rdf keyword

Google can also do (albiet while triggering annoying ‘are you a robot?’ captchas)…
‘

filetype:rss keyword

… which discovers a lot, but obviously not everything. So then you would need to use filetype:xml — and that would bring in all sorts of things which are not RSS feeds. Chaining inurl: seems the better option.

A simple universal comprehensive blog search, like the old Technorati, would be the better solution. But it seems no-one wants to build one, for some unknown reason.