Of course, the iPad 2 has far and away the largest market share, at 60 percent, but both the iPad and the "new iPad" account for 20 percent of all U.S.-based iPads seen by apps using Localytics for app analytics, after two months and 1 week of release.
There are some caveats to that. The measurement accounts for U.S. iPads, and it is also based on app usage for apps using Localytics for app analytics. It's not the same as a true measurement, but of reasonably close accuracy.
Since then the shift has been to 20 percent for the "new iPad," 60 percent for the iPad 2, and 20 percent for the iPad, showing that Apple's third-generation tablet is mostly cannibalizing the share of its eldest sibling.
The "new iPad" sports LTE (in Canada and the U.S. only), a faster A5X processor, a retina display, improved camera, and more. That said, it might have a long row to hoe to beat out the iPad 2; that model still sells in 16GB form for $100 less than the same model "new iPad" (wi-fi $399, 3G $529 vs. $499 and $629, respectively).
For many, the iPad 2 may still represent "good enough."