Lots of rumors about the A7M266 having problems, but it is hard to find confirmation. Most of the rumors seem to come from vendors who are having a difficult time getting stock of the A7M266. A whole bunch of similar posts were up here last week in response to someone talking with TC Computers.
The A7A266 should be Asus' board made with the Ali DDR chipset instead of the AMD 761. I haven't seen anything about an official release of this board yet, but it sounds like the Ali board will be Asus' "budget" DDR solution alongside their boards with the via KT266 models. There is some info about performance improvements in the Ali chipset with the latest beta BIOS version over at http://www.lostcircuits.com/motherboard/iwill_ati/. This is the IWILL board from that chipset, but it should give you some idea.
A scientist will never show any kindness for a theory which he did not start himself. – Mark Twain