Configuration Settings

I am looking to have my business rules dll read a key from the web config file using ConfigurationSettings.AppSettings. So far my dll which is shared by two test apps seems to get the right value depending on the calling app. Are there any issues doing this?  I had the settings in the registry but now we are going to have two or more web apps using the library so I want to read a key out of the config file. I don't want the apps to have to pass this to the dll.