I have spoken previously about indirect configurations and tried to convince everyone of how useful they are.
I noticed something today concerning indirect configurations that quite surprised me. If you execute a package that uses an indirect configuration and the environment variable is not present you get the following warning:
The configuration environment variable was not found. The environment variable was: "Seer.ConnectionManager.CUECommonReference". This occurs when a package specifies an environment variable for a configuration setting but it cannot be found. Check the configurations collection in the package and verify that the specified environment variable is available and valid.
I was surprised because I would have expected the package to throw an error rather than a warning. I questioned this and Matt David from the SSIS team replied here: http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=425031&SiteID=1
You kinda get the feeling that it might have been decided with the toss of a coin :)
Regardless of that, its just something to be aware of. If you forget to deploy your environment variable then you will not get an error.
That is all.