Patch 1.0.3a is primarily a bug fix patch. Primarily, zombie Bears will no longer be afraid of enemies on slopes and pathfinding’s been greatly improved—they’ll no longer make fools of themselves by sticking onto objects that they shouldn’t be colliding with. Some unspecified gold and service exploits have also been patched… sorry cheaters.
There is also one design update that comes with 1.0.3a. Fans have complained about the raised repair costs that were implemented in 1.0.3. As a result, Blizzard’s reduced the amount of wear-and-tear done to armor in regular combat. The 10% reduction in durability on equipped items taken as punishment upon death has not been altered.
As usual, Blizzard’s made their patch notes readily available for reading on their site.