If you have any snap-in instance lists, they will now be running in DirectX mode, so you should test carefully that your snap-in instance lists still behave the way you want. DirectX mode instance lists will look different and may behave differently.
In particular, in DirectX the list's current item changes as the user moves the mouse over it, and the source fields of the list columns also change. Previously (Win32 mode) the current item changed only when the user clicked on an item.
Also check that your instance list resizes correctly. This can be a problem if your snap-in list has W32 controls (including ActiveX and the List View) that are not directly sized by the parent object's layout manager.