I recently noticed that when downloading an application, Safari doesn't give the warning it used to. I have deleted the .plist file with no change. Using Mac OS X 10.5.8, Safari 4.0.4. Any ideas why and how to re-enable?
I'm not sure if you're referring to the security measure where Safari opens "safe" files after downloading. That's available in the General tab of the Safari preferences.
As far as downloading applications goes, that warning is attached to the application itself. Let's say you download a DMG with an application, and then move that application to the Applications folder. When you run that application for the first time, you get a warning mentioning that this is an application that you downloaded from the Internet. The upside of this is that it works whether you use Safari or not.
Do you see this warning when you download applications and run them for the first time?
(Image snagged from here after a Google Image search.)
Is the checkbox for "Open "safe" files after downloading" still checked? If it's not it won't warn you.