The Times paywall went up yesterday afternoon.
If you've been using the Times iPad App, you can still get access to the "Top News" and "Most E-Mailed" articles without a subscription. But access to any of the other sections (ie. business, technology, sports, opinion, etc.) will have a little black square next to it, indicating that a Subscription is required to access the article.
Clicking on one of these sections will take you to a screen which invites you to sign up. Once you do sign up via their (somewhat clumsy) in-App purchasing system, it updates the App to allow full access.
If, however, you've been accessing the New York Times via the website (using Safari) - then you wont hit the paywall till you reach the 20-article threshold. Reaching articles via external links don't generally count towards that 20-article number.