How do I change the default Space for an app in Mission Control? Under Snow Leopard and Spaces you could define which Space an app should automatically launch in, including the ability to indicate that it should be visible in every space.

My apps are respecting the settings I applied before upgrading to Lion -- for example, iChat, QuickTime Player, and my Billings time tracker show up in all Spaces, Chrome always launches in space 2, etc. -- but there no longer seems to be any way to modify them or add these kinds of defaults for new apps.

Is there any way to make these assignments with Mission Control?
You can do this from the dock.

Switch to the space you want to pin your app to, then access the options menu from its dock icon: