World-of-warcraft – Goblin apprentice mount, where to get it

As of Cataclysm, you can now acquire Tome of Polymorph: Turtle by fishing. It's a random reward from any school of fish in the new level 80+ Cataclysm zones (Mount Hyjal, Deepholm, Twilight Highlands, and Uldum).

As was discussed in this question:

Hit is the premier secondary stat for rogues, especially so for assassination rogues, as a larger portion of their damage comes from their poisons, which use spell hit.

You don't need to reach the so called "hit-cap", but until you reach the spell hit cap, theorycrafting indicates your next best secondary stats are mastery, and then haste.

Expertise is of minimal overall importance, beating out only crit in terms of estimated overall worth. (See here)

In short -- do not reforge anything into expertise -- you're better off reforging into hit or mastery (do note that the amount of hit rating you need to reach the caps are lower than what the Elitest Jerks link shows, as they are primarily considering raiding, which involve higher level'd bosses.)