A really nice (and funny) article why you should not do this, by Tyler Holmes.

http://blog.tylerholmes.com/2008/10/don-set-your-sharepoint-app-to-full.html

I came across this article because we had an assembly containing a feature reciever that would cause an error when executed.
Assemblies containing feature recievers should always go in the GAC (by design), but we where creating a custom policy.

So, I agree with Tyler that custum policies are still preferable, but when you have a dll that contains a feature reciever, you should just put it in the GAC.