Discovered this myself earlier today. Something to note only as a clarification, you can create these subfolders within the RSS section itself as opposed to 'On my Mac'.

Also note, Smart Folders will only really allow searching for something like 'message type is feed' and 'message is unread' but not 'message is in mailbox' if the folders are in the RSS section

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I know, replying to myself, for shame.

For those that are a tad lazy with their Feed reading and instead read a headline, think, "I'll read that later" and skip to the next headline. You can end up with a lot of unread posts in your feeds that go back weeks. This is especially a problem with those rapid-fire team posters (Coudal, Boing-Boing I'm looking at you).

So, I adjusted my Unread Feeds Smart Folder to include 'message received this week'. Try it, it takes the weight off.

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