An interesting detail when you migrate VB6 to .NET or web is the MDI implementation.
For example the following case.
If you have a MDI form and a MDI child, both with menus. When the child is shown, its menus are shown in the MDI form instead of the MDI form's own menus.
This behavior is exploited on some apps to be able to have different menus depending on the form that you are currently using.
So just put attention to those details when you are migrating to web :)