ReadBurner
Readburner has debuted, and it appears to be a competitor to services like Friendfeed.
The tabs at the upper right allow the user to toggle between the user’s account at Google Reader, and a stream of the shared materials from that, integrated with a comments capability derived from Disqus, the blog commenting solution.
I haven’t determined yet if the Disqus integration means that comments made in Readburner on posts made in blogs that use Disqus comment management would lead to the Readburner comments showing up on the blogs as well as in Readburner. That would be a very wise thing to work through, and would reflect the natural gregariousness of flow apps back into the blog foundation that supports much of the conversational sociality going on.
[Update 15 Apr 5pm ET: Drew Olanoff of Feedburner has responded in the comments here, stating that it is their intention — and that of Disqus — to be able to ‘streamback’ comments into the original blog posts.
By ‘streamback’ I am drawing on the original ‘trackback’ term, but intending the image of pulling these comments from the ‘stream’ that flow apps implement. Note that the same sort of streambacking could take place from Twitter, Pownce, or Workstreamr, or any other flow app… and eventually probably will.]
Here’s the Google Reader tab, which looks like a reframing of the Google service:
.flickr-photo { border: solid 2px #000000; }.flickr-yourcomment { }.flickr-frame { text-align: left; padding: 3px; }.flickr-caption { font-size: 0.8em; margin-top: 0px; }

ReadBurner’s Google Reader Tab, originally uploaded by Stowe Boyd.
I added a comment to a post:
.flickr-photo { border: solid 2px #000000; }.flickr-yourcomment { }.flickr-frame { text-align: left; padding: 3px; }.flickr-caption { font-size: 0.8em; margin-top: 0px; }

ReadBurner, originally uploaded by Stowe Boyd.
In the following figure, you can see the stream of shared posts, but since the service just went live there is little or no commentary, so it is difficult to contrast with Friendfeed or Alert Thingy, the new client for Friendfeed.
.flickr-photo { border: solid 2px #000000; }.flickr-yourcomment { }.flickr-frame { text-align: left; padding: 3px; }.flickr-caption { font-size: 0.8em; margin-top: 0px; }

ReadBurner, originally uploaded by Stowe Boyd.
But it looks like Readburner has adopted the (bad) convention of concealing comments underneath a “(13) comments” hyperlink. They should simply expand that in place, as Friendfeed does, or more aptly, as flow apps do.
Comments shouldn’t be buried in a second-class citizenship: they are first class elements of the conversational flow. Don’t create these two kinds of items. Everything is just an utterance, although some have links in them.
Looks like an interesting experiment, and if they tweak it, it could motivate me to go back to Google Reader instead of rattling around in Friendfeed and Alert Thingy.