Event driven JS tends to go spaghetti really quickly unless you're using a good events framework. The yui3 and sproutcore frameworks are pretty close to opposit

Event driven JS tends to go spaghetti really quickly unless you're using a good events framework. The yui3 and sproutcore frameworks are pretty close to opposite ends of the spectrum in terms of philosophy, but both have very well defined processes for dealing with events. The two frameworks you mention are fine for adding "ajax" to a more or less working server based app but they aren't so hot for building a complete app. FWIW, MochiKit's Signal framework is also nice (though the codebase is now fallow) and Dojo's system has a sort of nifty aop feel, but dojo is kind of hairy in that there are a lot more chefs in the kitchen there.