I gave it a shot. I hoped it would work. Unfortunately, I’ve become hooked on NetNewsWire Lite over the years.

My main gripes with the RSS/Atom support in Mail on Leopard are:

• It’s a pain to import OPML files. I posted a fix for that, though.
• The arrow keys aren’t incredibly useful for navigating between panels, through feeds and items, like they are in NNWL. Having to use my trackpad is lame. Having to tab focus on panes is bad.
• I haven’t yet seen any way to customize the display of feeds in Mail. Not a biggie, but the default view is kind of blah.
• Sorting seems to be alphabetical only.
• When Mail is handling more than a couple of accounts (especially IMAP with server-side folders) it’s invariable that you’ll have to scroll to see your feeds. I’d rather Apple+Tab over to NetNewsWire Lite or Vienna.
• It’s called ‘RSS’ instead of ‘Feeds’ or similar. This might seem nit-picky, but it’s like calling all computers ‘Windows’ instead of… computers.

I like the idea of having feeds in my Mail reader, aggregating the bulk of my passive reading. It’s kind of like using Adium to group all IM-type accounts (I don’t, but I see why folks do it).

Currently, the feed support in Mail is fine if you subscribe to one or two feeds I guess. The UI just isn’t conducive to someone with hundreds of feeds that are updated frequently.