Now I am going to tell you Plus Manager is finally meeting my original goal.
I had been waiting for a tri-state tree view control for so long until I met this article in 2006. However, BDS 2006 was targeting .NET 1.1 so this control cannot be used.
The design of this control is so wonderful that it looks natural and beautiful. Thanks Uwe for creating Zeta C# Library which contains this useful control.
Now you can see that I use both Office 2007 renderer and Tango icons here.
BTW, I modify the original source code in order to make the tree view Vista-aware.