The ConfigurationSettings.AppSettings class became obsolete in Beta 2.0, replaced by System.Configuration.ConfigurationManager.AppSettings. This stumped me, because ConfigurationManager was nowhere to be found. You have to add a project reference to System.Configuration for it to show up. Here's the google thread. Thank you, Brett Hobbs.
Another tip on using AppSettings in Windows Forms Beta 2.0 is to put configuration values you want to read with ConfigurationSettings.AppSettings[] in the good ol' appSettings area, which you'll probably have to create. I tried to place them in the applicationSettings section and kept getting null object reference errors.
Golly. Now that I figured that out I can walk the dogs. They've been ticked at me for the last hour after I told them I couldn't do something as basic as read from an application config file. That look of disgust in their eyes...