It was relatively easy, although still more difficult than I would have guessed, to hook my bespoke website's Atom feed up to Google Buzz. I already have a Google email account and associated profile so Buzz just showed up in my Gmail interface. Setting it up it offered to connect to my YouTube account or my Google Chat account but I didn't see an option to connect to an arbitrary RSS or Atom feed like I expected.
But of course hooking up an arbitrary Atom or RSS feed is documented. You hook it up in the same manner you claim a website as your own via the Google Profile (for some reason they want to ensure you own the feed connected to your Buzz account). You do this via Google's social graph API which uses XFN or FOAF. I used XFN by simply adding a link to my feed to my Google profile (And be sure to check the 'This is a profile page about me' which ensures that a rel="me" tag is added to the HTML on your profile. This is how XFN works.) And by adding a corresponding link in my feed back to my Google profile page with the following:
I used this Google tool to check my XFN connections and when I checked back the next day my feed showed up in Google Buzz's configuration dialog.
atom:link rel="me" href="http://www.google.com/profiles/david.risney"
So more difficult than I would have expected (more difficult than just an 'Add your feed' button and textbox) but not super difficult. And yet after reading this Buzz from DeWitt Clinton I feel better about opting-in to Google's Social API.