— Marshall Kirkpatrick
That's an understatement.
The one thing common to feedreaders, Twitter and Friendfeed: they order articles by time, and so incent people to post often. Keep posting, and your stuff is more likely to show up on people's screens. They become more likely to click on it, retweet it, share it on google reader, like it on friendfeed.
It can't be complete junk, of course; if you spam people they'll unsubscribe. But keep posting mediocre stuff and they won't.
In fact, people grow more tolerant of mediocrity in their feedreaders. Subscriptions have a way of getting out of control. Past half a dozen sources people lose track of what they're reading, and of who they've subscribed to. You can slip lots of crap by their eyeballs before they take the time to reorganize.
Some of your readers will give up on the medium for a time. They'll jump to the next great thing, somewhere along the facebook-twitter-friendfeed trajectory, and they'll find it works so much better! They'll think it's because of some shiny new feature in the new tool. They'll never realize it's just that they're subscribed to less crap. So they'll start subscribing to crap again, and the cycle will repeat.
A cynical strategy to game this world: write one smashing post every week or two, use it to get new readers. Interleave the smashing posts with hundreds of short, simple, unique pieces. They will keep you in the eyes of your readers once they've subscribed.
Even if you aren't this cynical, these are powerful and subtle forces. Most of us aren't pushing a brand or an agenda, and may not think we care much about clicks and links and shares. But we respond to social feedback. If more frequent posts yield more feedback, we post more frequently. It's easy to see the benefits, harder to see the ill-effects.
And ill-effects there are. When our reading is sorted by time, nobody reads. A conversational medium requires that its participants be good listeners. The alternative is monologuing, the realm of exhibitionists, clueless advertisers, and spam. When we're incented to post more frequently, the world gradually degrades to an advertising free-for-all. A garbage-in garbage-out world; fewer people saying interesting things; less diversity in what we read and who we read.
By shirking our reading we're poisoning the well for ourselves. Things must improve.
It's amazing how settled time-order has been in Web 2.0. Twitter is entirely realtime. Facebook has lots of filtering options; it's unclear who uses them. Friendfeed's 'best of day' view is a big improvement, but it is hamstrung in two ways. First, it isn't the default, so most people never see it. Second, it changes slowly and you can't page past the first page, so there isn't as much to read. If you read a lot of stuff you will find yourself returning to the time-ordered view.
Friendfeed has a second mechanism to manage volume: it allows you to organize your subscriptions into 'lists'. Google Reader's folders are analogous. Folders help manage the volume/value tradeoff; make sure you read the low volume feeds, then dip your toes into the torrent to taste. They're still a static organization, though. Removing a feed from a folder isn't easy to do while reading, so we put it off, and our folders pile up cruft (if we ever bother cleaning them up).
The cynical blogger gaming the system to stay in his reader's feedreaders need change nothing when feedreaders get folders. For the reader, removing a feed from a folder is as static and as hard as unsubscribing.
The good news is that things are easy to improve. When I built my own feedreader, it was amazing how quickly I preferred it to Google reader. A simple policy of fairness—I never show two stories from the same source—sufficed to compensate for nifty UI features, search, and social recommendations. One can do much more.
Update May 19: Gabor Cselle's built an iPhone app with a prioritized order for email! Leaving time order behind is not just for web 2.0 social tools.
Update Jun 6: Fred Wilson's comment points out several twitter apps to sort by popularity.