We've been seeing this GDKP thing sneak up on the forums and elsewhere a lot lately, and while Scott has mentioned it (in a somewhat disparaging way, in fact), we haven't really taken a good look at it yet. So let's do so. GDKP stands for Gold DKP, which is kind of a mishmash of acronyms. DKP, or Dragon Kill Points, are a very popular way of determining loot division in a raid -- the concept dates back to earlier MMOs, and involves players earning points per boss kill that they can then spend on gear. We've talked about other DKP systems before. But rather than awarding loot based on arbitrary points, Gold DKP, as you may have guessed, instead gives loot to the player willing to pay the most gold... to the other players in the raid.
The way it works is this: You go into an instance, say Naxx, and everyone knows ahead of time that it is a "GDKP run," or a "gold run," or a "cash run." You down the first boss, and Webbed Death drops. The master looter then takes bids of gold on the item (this can be done via public chat or via an addon), and whoever bids the most gold gets the item. The person who wins then pays that amount of gold (some raids have minimum bids of, say, 100g) to "the pot," and the raid moves on. Another boss drops, another item drops -- usually all items, including recipes and mats, are auctioned off -- and another high bid goes into "the pot." Then, at the end of the raid, the pot is evenly split among all members. Everybody who joined in on the raid gets an even share of the bidded gold, including people who got no items, or the Mr. Moneybags who won them all.