It's not as responsive as Sencha Touch, which is the best out at the moment, but Sencha Touch is noticeably less responsive than native apps. It's noticeable enough to where you can't design mobile apps that are native-looking because they aren't responsive enough. Plus theres little stuff like flickering that get in the way.

I would say the problem is not in these frameworks, but in the browser. It wasn't made for these kind of apps and it is slowly catching up.