Control State
I'm finishing the Luis Abreu's ASP.NET 2.0 book, and he speaks about de Control State feature. This is a very cool feature, because the server side controls don't save the important information about your functioning in ViewState.
In 1.x ASP.NET versions, this information is stored in ViewState, so when the ViewState is disable, some controls doesn't work correctly. For example, disable the View State and try to change the index pagination of the DataGrid control. You’ll see that the control will disappear.
With the ControlState, this important information is stored in other place and if you disable the ViewState, the control will continue to working normally. To disable the ViewState is very important when you don't preserve the control state during the postbacks or when the performance of your application is low.