There has been an official declaration that portions of the Insane in the Membrane achievement will not be obtainable come Cata. There is no word yet on whether those who have completed those portions ahead of time will be able to complete the remaining portions or not but this muddy water is not stopping the truly Insane last-minute achievement seekers.
One of the requirements of Insanity is to be Honored with the Bloodsail and Exalted with all of the Steamwheedle Cartel, each the sworn enemy of the other. Contrary to popular belief, the two reputations do not have to be held concurrently in order to obtain credit, significantly decreasing the amount of grind this portion of the achievement has historically been.
Since most of the Insane-seekers are also working toward the Exalted achievement, it is far better to gain the Bloodsail rep first and lose it in favor of the Exalted reputations with Steamwheedle Cartel. This requires slaying Booty Bay guards and NPCs until Honored with the Bloodsail is reached and then turning in repeatable quests with each of the goblin cities to repair rep to Neutral before heading back to the pirate or DM grind.
Those who are Bloodsail Admirals but not Insane-seekers may also be interested in repairing their reputation now: Beta's Booty Bay has level 85 elite guards who crushing-blowed my poor turkey for 17k worth of damage a swing.
Each city has a different quest and each quest requires 40 cloth and 4 of some type of trade good (runecloth and coal for Everlook, for example). Each turn-in provides 500 rep for that city and 250 spillover rep for the other three up to Netural. Getting your first city to neutral will have your other three halfway there, so half as much cloth is needed for the next city, etc. In the end you'll need
~ City 1: 84 turn-ins (3360 cloth)
~ City 2: 42 turn-ins (1680 cloth)
~ City 3: 21 turn-ins (840 cloth)
~ City 4: 11 turn-ins (440 cloth)
for a total of 6320 cloth. Everlook requires Runecloth, Gadgetzan requires Mageweave, Booty Bay requires Silk, Ratchet requires Linen. In the end, this is a lot of cloth required to get back to neutral with all four cities.
Of course, a true goblin would sell you the cloth required to get back into their favor, right? Prices on my server have already increased drastically for these cloth types due to normal buyouts of the lower-priced stuff and there is very little left on the AH at all. Now is the time to consider offloading your cloth.
You can start by sending me some while I try to repair my own reputation.