Techmeme added an interesting feature a few days ago. It wasn't announced publicly, so I'm not exactly sure how it works, but I'll take some guesses and hope that they get corrected by people in the know. 

Here's a screen shot of the current Techmeme site, with arrows pointing at tweets appearing in the discussion sections. 

http://scripting.com/images/2011/02/10/tmscreen.gif 

1. Techmeme maintains what they call a "whitelist" of Twitter accounts that they regularly read looking for links to pieces that are currently on Techmeme. These people were chosen presumably because their comments tend to be interesting or influential. These were editorial choices. 

2. At first I thought the links had to use Techmeme's url-shortener, but now it appears that is not true.  

3. When a comment appears, a link to it is added in the "discussion" section under the post. 

4. Tweets can now be first-class items on Techmeme. 

It's interesting that Techmeme has effectively become a surface for Twitter, organizing tweets by topics that are of interest to their readers. It's not certain that this will be compelling, and that the attention from Techmeme might influence what people say.  

A few years ago, when flow-hungry bloggers realized that appearing in the "chorus" on TM could result in significant flow, you could watch a story percolate through the tech blogosphere. At times it got ridiculous as people struggled to find something interesting or original to say. That could be even more difficult when 140-character constrained. 

Other publications should watch this experiment carefully. Even if it doesn't work with Twitter, it's an interesting model for what an integrated news system might look like in the future.