The main problem with going all into the cloud for me is that the mobile experience for HTML + Javascript apps on mobile devices is just not good enough. They're too slow, the device access isn't as good, the framework support isn't there (especially when you want your app to really fit the unique styles of Ice Cream Sandwich and Windows Phone 7).
As a result, it forces a small developer like me to create a client and a cloud version. That's just too much work, so I tend to be client-only.
