As said previously, it's not Apples to Apples, but it still is pretty remarkable considering NYT is not only a nation-wide pub, but a world-wide pub.  I think people see the 'money making' prospect of Twitter, and instead of paying for an ad on NYT, you can get a FREE twitter, and spread the word that way.

- Notimeforrecess.com

I regularly work on online promotional campaigns for a number of clients and I track the traffic referral from many different sources.  The popularity of Twitter and the the ability it provides to target a specific audience makes it surprisingly effective.  In my experience, Twitter may generate more referral traffic to a client's site than a New York Times or Wall Street Journal placement.  This is shocking when you consider the enormous reach of NYT and WSJ. 

The main things I use to track referral traffic are Google Analytics and bit.ly

I would be curious to hear what other people experience.

People have been predicting that the internet would take over print.  Already had, so it is not suprising that twitter acquires more users in April compared to the online version of these newspapers.  Newspapers don't interact.  They just post news, sometimes biased.  But a tweep can post what "they" think is relavent and other tweeps who agree will then retweet to show their support of that news or information.

I beleive that twitter would have eventually made this impact with or without celebrities.  It's the "average Joe" that drives twitter forward, not celebs.

IT. COULD. GO. ALL. THE. WAY.

I believe a good part of Twitter's existence and it's success is due to the fact that content is a good part of what drives it..
It's an avenue for information facilitated by the Twitter "engine" which is both the actual utility "Twitter," and the people that tweet.

The graph shows audience (unique visitors) not user sessions (unique visits). Just a minor detail, and doesn't detract from the fact that Twitter is touching more people than NYT or WSJ.

Add to that the fact that a whole heckuva lot of Twitter users rarely hit the hyper-text-transferred-to-the-browser page, but rather use through a desktop and/or mobile app, and the figure gets even more impressive.

But, we're not comparing apples to apples here. Both NYT and WSJ are content driven sites, and Twitter is a utility. That's like comparing the customers of a retail store to those of the cable or power company. An interesting comparison, but not absolutely relevant.