Of all the features added to WoW since it launched, which do you rate the highest?
For me personally it's the Dungeon Finder/Raid Finder tool. I can't even begin to imagine how we used to form groups back in the old days via the chat channels. The whole 'LF 1 DPS UBRS' type spamming until someone whispered you and the group was formed. And then waiting for the person to arrive at the dungeon. They of course had to be on your server too.
Now you just queue, wait and viola. In some ways it's a shame you don't even have to talk to the other people now but ultimately I think it's a huge feature that changed the game for the better. If my memory serves me right it wasn't implemented until Wrath yet it feels like it's been around forever.
So bravo Blizz for that.