When flashing one of a house's biggest potential leaks—where the eave overhang meets a vertical wall—contributing editor Mike Guertin chooses to err on the side of caution to control water flow and not rely solely on step flashing. As part of his multilayer approach, Mike applies housewrap, flashing tape, copper, self-adhesive membrane, and a kickout diverter. The kickout diverter directs water into the gutter decreasing the odds it will make its way behind the exterior cladding. A kickout diverter is not only best-practice when flashing the eave edge to a wall, it's code. The 2009 IRC includes the following section: 905.2.8.3 Sidewall Flashing - "At the end of the vertical sidewall the step flashing shall be turned out in a manner that directs water away from the wall and onto the roof and/or gutter." That's code-speak for a kickout diverter.
To learn more about Mike's flashing technique, read Flashing Troublesome Eave-to-Wall Intersections from Fine Homebuilding issue #202 (April/May 2009) pp. 106-110.