I map the letter D to TOOLS/VIEW/ROTATE. When I hit the D key the cursor turns to two arrows chasing their tails. When this cursor is placed over a vertex in the model and clicked it will change the rotation point from the global Origin to the selected vertex. The Rotate tool also works with linear edges providing rotate about axis. This functionality is invaluable when working on complex assemblies and models in which the origin is far away from the solid body.