I will be the first to admit that jQuery is much better for the majority of websites. This is intentional. Everyone and their mother has already developed a JavaScript libraries for making the DOM tolerable and AJAX calls a bit nicer, and some of them do a great job of it (e.x. jQuery)

Cappuccino shines when building more complex, primarily client-side, web applications (like 280Slides and Atlas itself). We realized Cappuccino couldn't be everything to everyone and decided not to make sacrifices to attempt that.

In the past most people have ended up building these kinds of applications from scratch (Gmail, Google Maps, Docs, Meebo, Zoho, etc), often implementing their own framework in the process. Cappuccino attempts to provide solid foundation on which to build a very "rich" client-side application.

It's true the learning curve is a bit higher than jQuery, but I think that's inevitable given the types of applications you typically use the technologies for. Atlas is one thing that should help with that. And Cappuccino's documentation could definitely use some improvement.

I've asked before, but I'll ask again: if you know of an application of the kind I'm describing that's built using jQuery I'd love to hear about it, I am curious.

I'm not crazy about the OSX look either (is it skinnable?) but I liked the responsiveness of the demo apps. Also generally all entries are welcome to this space - it's anything but a solved problem.

We now have two themes, the "default", which you see in 280 Slides, and the new "Aristo" theme we announced with Atlas (designed by Sofa: http://www.madebysofa.com/)

Aristo is designed to "feel at home" in Mac OS X and Windows. Does it look too much like OS X for you, or are you talking about the 280 Slides theme?