Turns out it's easy. Just create a text file called com.apple.DownloadAssessment.plist under Library/Preferences in your home directory, with the following content:
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>LSRiskCategoryNeutral</key> <dict> <key>LSRiskCategoryContentTypes</key> <array> <string>public.item</string> </array> </dict> </dict> </plist>
Then log out and back in. Done.
For details of how this works, see the following:
Update: The instructions for Snow Leopard are slightly different.
Tue, 06 May 2008 23:03 UTC