Diablo 3's servers have come back online earlier than expected, bringing big changes to the game with patch 1.0.3, as promised. Primarily in response to player concerns, many of the changes tweak high-level item drops, reevaluate Inferno difficulty, and make drastic reductions to crafting and training Artisans.
Players who have unlocked the "Inferno" difficulty will be more impacted by today's sizable update. According to the patch notes (after the break), difficulty in Acts 2-4 have been reduced to be more in line with Act 1 – which is no slouch.
Repair costs have also seen a substantial increase for level 60 players/gear, making death a costly scenario and killing our hopes of grinding out Whimsyshire pony runs for top-end gear. One welcome change is tweaks to champion packs and their loot drops; guaranteeing rare drops in some cases (specifically when defeated under five stacks of Nephalem Valor).
Currently, the auction house feature is offline. Joystiq has contacted Blizzard to find out when it will become active again, but has yet to hear back at the time of publishing.
If you're not familiar with Diablo, then this might help explain how the game works: click, click, click, click, click.
Update: The Auction House is back online.