In the ESRI Web ADF for the Microsoft .NET Framework the default behavior for the mouse scroll wheel is to zoom in to the map control as you move the scroll wheel forward. Enter the following code snippet in the Default.aspx after all the Web ADF control declarations in your web application if you would like to change the behavior of the scroll wheel so that it zooms out as you move the mouse wheel forward (which is also how ArcGIS Explorer behaves).
mouseWheelAwayZoomIn = false;
Here is an example of the default behavior: http://serverx.esri.com/bendenaquadsp/
Here is an example of the changed behavior: http://serverx.esri.com/bendenaquadspreversescroll/