I prepared a hosted app last week. Very easy. All you need is a manifest, an icon and a screenshot and you're done.
What about if the game or site requires registration?
jan – there is a licensing API that should account for that. I'm not sure how it works.
I prepared a simple installable one. If you want to distribute the whole app as installable and runnable offline, you just have to load all the source files into a directory and add the extra stuff. Fairly easy. Get on the chrome dev channel to test it.