One way to describe ReadBurner is that it's adding value by and on top of aggregating explicit attention gestures. Below are some thoughts on ReadBurner and what it could do to be even cooler.

Opt-in as the way to do it

While Google Reader recently screwed the...well, dropped the ball, by pulling in Shared Items from your GMail contacts whether you liked it or not - ReadBurner is a good example of the kind of opt-in sharing that is much more consistent with user-centric leveraging of Attention Data. That's the polite way to say that most people will never find out about it. Just kidding.

Vendors need to learn that the era of lock-in is gone and much of the data-centric innovation of the future will probably need to be opt-in only. People have always believed that forcing others to do your bidding is the best way to get things done, but when power parity is approached - coercive steps like opt-out data sharing breaks a social contract that users are no longer tied to by necessity. We can leave and go somewhere else, so you have to get our permission to use our data.

That's probably overstating the situation - do Twitter users need to opt-in in order for API driven services like Twittertale (NSFW) or Twitterwhere to use their tweets? Hopefully not. This is a complicated question, but starting with opt-in seems like a good idea, generally. (I smell a forthcoming blog post on this question itself.)

Risks taken

Marktl seems intent on pushing the envelope with the application; his logo originally used the Google colors and now he's experimenting with running AdSense next to the content - including against the full feeds! That's something even Google hasn't dared to do yet. That move doesn't seem so wise to me given that it's the supposed tech savvy nature of Google Reader users that Marktl says make Google Reader shared item feeds particularly...tech savvy. Such users are widely believed to be the least likely to click on ads.

Marktl is adding submitted feeds manually but I've submitted my personal link blog from Ma.gnolia because Google Reader doesn't deal well with accounts subscribed to more than 1k feeds. I'd like to participate in ReadBurner too. If it's tech savvy users you're looking for Google Reader is not the be-all-end-all by a long shot.

Recommendations

ReadBurner is a great example of one of the cool things you can do with feeds. Here's some next steps I'd love to see from the app.

Recommended users. Let me sign up for an account with ReadBurner (using or tied to OpenID please) and recommend other users' feeds to me that have a lot of overlap with mine. Something like the recommendations at ShareYourOPML (site down) but dynamic so people will keep using it. I'd love to get a feed of newly recommended users too, and perhaps the ability to add recommended users' feeds to a spliced feed just for me.

Hot users. I'm guessing that ReadBurner could show me a LeaderBoard of the contributors who most often share items early that end up being hot later. I would subscribe to those peoples' feeds in a heartbeat. The site has some interesting stats now, specifically the most shared-from sources and authors, but a lot more is possible I'm sure.

It's exciting to think about. This is the kind of innovation that gets the mind spinning. I hope ReadBurner will continue developing, will see continued adoption and won't be shut down by Google. Goodness knows someone outside has to keep the pressure to innovate on Google Reader - remember how long it took GReader to add a search box? Google Reader is very good, but so much more can be done.