Is there a way to block certain apps on a Droid?

[Mariusz Symkow]

I think this is what you are looking for:

Go into the Data Usage section under settings, then click the app that is causing trouble. Check the box that says 'Restrict background data' and then, when you are not using that app, just go into the app manager (Settings > Apps) and force close it. That's the way without any apps, and I do not know of any apps that can do this. So, if you want it to be automatic, I'm not the one to ask.