In the early days of CSS-based design, square corners were a hallmark of designs that focused on simplicity of code, rather than visual aesthetics. Rounded corners remained somewhat painful to use, however, until the emergence of support for creating them using the border-radius property of CSS3. Now it takes only a few lines of simple CSS code to have nicely rounded corners—as long as you can accept that many users will see square corners until they move on to more modern browsers.
A Book Apart, the young book-publishing arm of the organization behind A List Apart and An Event Apart, has just released CSS3 for Web Designers, by Dan Cederholm, as a guide to CSS3 from the "what's really useful right now" perspective. As with the company's first book, HTML5 for Web Designers, this orientation, combined with an expert author, takes a large, complex subject and reduces it to a small, readable book.
You probably know of Carsonified from its Future of Web Apps and Future of Web Design conferences, or perhaps from its ThinkVitamin site. Now it has added Think Vitamin Membership, which offers a series of videos on a variety of leading-edge web topics.