I developed a few toy projects to learn each framework. Cappuccino is an incredible technical accomplishment. I've done iPhone development, and it's true that

I developed a few toy projects to learn each framework. Cappuccino is an incredible technical accomplishment. I've done iPhone development, and it's true that you can easily map your Cocoa experience onto Cappuccino. However, when I hit a corner case such as embedding a SWF, the abstraction leak was a nightmare. Sproutcore feels safer because it doesn't hide the fact you're working with HTML/CSS; you need to write it to create custom views. Inserting a SWF was straightforward. The other reason I favor Sproutcore is the feeling Cappuccino has cargo cult issues. For example, Sproutcore uses namespaces while Cappuccino just prefixes initials. In Sproutcore you have "SC.Object" while Cappuccino uses "CPObject." Cappuccino is still pre 1.0, so all of this could change, but if I had to choose a framework to write an app today, I'd go with Sproutcore.