I think the problem that most people have who are upset about this change is that they're actually using the dock and cmd-tab to switch between applications. Using an app launcher like alfred makes the concern trivial, as switching to an app and launching it use essentially the same action. In that sense, this auto quitting feature is actually a nice compliment to that type of workflow.
That's a ridiculous statement. Using Alt-Tab isn't my 'problem', it's a very efficient way to cycle between a few apps in heavy use.
In general I appreciate Lion's approach to quitting/restoring things, but they have messed up the associated Dock and Alt-Tab behaviour. I wouldn't be surprised to see this fixed in an update.
