v1.0 - This was the initial release, which had poor voltage options and lacked mounting holes for water blocks.
v1.1 - Some of these boards have mounting holes, but the voltages were not changed, and there were no major revisions to the board. Thus this version is no better then v1.0!
v1.2 - Here is the revision that Abit should have started with! It has greatly improved voltage ranges for overclocking. The pcb color of the board was changed from a dull brown to a bright orange, making this new version easier to spot. A handful of these boards received the new revision nForce2 chips due to a shortage of the old chips, but they are not guaranteed to run at anything above 166mhz fsb.
v2.0 - Abit introduced this version shortly after nvidia released a new revision of the nForce2 chipset, which supports 200mhz fsb speed with no modifications. The board is unchanged from v1.2 with exception of the new chipset, and the only specification difference is the official support for 200mhz fsb speed.