Ghostcrawler made a sobering announcement the other day on the forums when he stressed to players that if they wanted a quest reward, they had better obtain it soon as Cataclysm will basically wipe the slate clean and virtually all quests from the old world will be changed. It only makes sense, after all, as the new race and class combinations will necessitate peppering the game world with the proper drops and rewards, such as ranged weapons in Elwynn Forest or Tirisfal Glades.
Some of it might just be re-itemizing the quest rewards, but I suspect Blizzard has pulled out all the stops and made quests -- especially starting ones -- far more creative and interesting than the basic kill X creatures or FedEx deliveries from five years ago. With so much experience under their belt as well as new tools and technologies, the new starting areas and the rest of the Cataclysm-wrought world is ripe for a more engaging questing experience. Be prepared for everything you know to change, so even if you've leveled like ten characters to 80, expect to chuck all that familiarity with old world quests out the window. That means if there are pretty trinkets from quests that you like, these are the last few months for you to get them.
I know, a few months sounds like we've got a ways yet, but time zings by quicker than we realize. What quest rewards would you like to grab as keepsakes of the old world? I'm fairly certain members of the Alliance are all rushing to get their Dartol's Rod of Transformation before it disappears forever. How about grabbing that Sprite Darter Egg from Feralas? The Horde just farm it as a drop, but why take chances? With all of Azeroth getting a facelift, Blizzard is probably going to change mobs and their drops, as well. Horde hunters might want to get that one last chance to tame Echeyakee or Sian-Rotam before the opportunity is gone forever. Quests will surely change, but I suspect rare mobs will be moved or disappear completely, too. I don't think Blizzard is holding anything sacred, which means we're running out of time to grab our souvenirs from vanilla. Quick, what will you be grabbing before it's gone?