For starters, there are a few bug fixes and class-specific tweaks (as I said, most related to the Death Knight class) but also new additions. For example, the racial restriction on mounts has been removed, player’s speed has been increased by 50% while in the form of a ghost and the Night Elf’s wisp form being boosted to 75% increased speed.
Also, this long awaited patch 3.0.8 brings to WoW fans 60 new graveyards scattered all over Kalimdor and Eastern Kingdoms, which means that player now have even more things to do in the game. If you want to know all of them, you can go read the huge full list of changes on the official page.