Do rules exist just so they can be broken? Maybe.
I'm just back from the 2009 Western Regional Barista Championship Finals. The spacious competition floor and plentiful seating allowed me a closer look than usual at barista technique. What surprised me was how one competitor after another (but not all), filled the basket, left a mound in the middle and then tamped without leveling off the mound. Most rapped the portafilter on the dosing fork once or twice to settle the grounds, but few leveled the coffee off.
The competitors were using doserless electronic Mazzer Majors with 83 mm burrs. Details here:
http://www.espressoparts.com/product/MAZZER_MAJOR_E/Mazzer_Major_Electronic_Espresso_Grinder__Doser__83mm_Burrs.html.
I asked some of them about this, and they said that the Major ground so evenly and the funnel distributed so well that leveling was completely unnecessary, even with a very visible mound. Nick Griffith, the winner, was one of the non-levelers.
Of course nothing is ever really settled in these matters. The employer of one of the competing teams assured me this was nonsense and that all of his baristas in the competition were leveling their doses.
I'll try a few level-free shots at home to see what happens.