As I mentioned, the biggest thing for me is the new skinning support. Curl now has a skinning application that lets developers make the interfaces look a lot more polished. The new skinning support uses style-sheets so that most designers will be at home in the environment. Because of the enterprise focus, Curl has always been great performance-wise, but the aesthetics left a lot to be desired. With the new support for skinning, people using Curl will be able to make applications that look good as well as run well. Another piece of this is the new rendering APIs. In addition to skinning, Curl now supports alpha blending and antialiasing. This should really help developers create engaging and interesting interfaces.
This is a big release for Curl and I'm glad to see they're chugging away and adding polish. They've been working to beef up their developer community and also have an RIA knowledge center with information on how rich Internet applications apply to business. This is still very much a company to keep an eye on.