SharePoint: Enable Error Messages

While creating my custom master page for this blog I failed to include a required ContentPlaceHolder on my page—and was shown a very generic "Error" message. Since I was never going to figure out what I had done wrong, I needed to enable error messages for my web application to get the full description of the problem (which solved my issue instantaneously). Here's how to enable turn off friendly error messages:

On the web server, navigate to the site directory (probably something like: C:\Inetpub\wwwroot\wss\VirtualDirectories\80 )
Open the Web.Config file in Notepad
Search for the safemode node with the word "CallStack" and change the CallStack status to true

Search for the CustomErrors node and set the mode to off

Save and close.
Don't do this on a live farm—it's not good for your security! But this is definitely a common change for development farms that will be sure to simplify your work.