Mirjam: Yea, once I seen the a1-a3 move - it is hard to counter. But if white is restricted from doing this (or similar), then black could gain the advantage by doing something similar.

As a side note, I hope they do not get upset for me posting the game - but this is one of the best games I have seen:

http://brainking.com/en/ArchivedGame?g=1089912&i=1

Between SueQ & Fencer - SueQ using the A1-A3 type of opening, and Fencer able to get past that and do some "damage". SueQ ends up winning by capturing enough of the pieces in the end.