DKP can be anything to any guild. Research the guild through talking to it's members or through their website.

My guild uses a DKP percentage based system w/ a cap of 1000 points. Basically whoever has the most DKP has dibs on loot but loses 50% of their acquired DKP. It gives new / more casual raiders more of a chance to get something since they don't have to take ages to catch up. Right now all of our setups are set to where one raid instance cleared = 100 DKP. So Kara bosses are worth 10 each (Chess doesn't count, not really a boss fight there :P ), Gruul is worth 60 & HKM is worth 40, you get the idea. If a raider attends a full ZA, Kara, and some 25-man clears in a week they'll be pretty high in DKP from just that.

We raid with an allied guild that does DKP a bit diffrently, they use a bidding and /roll based on the bids. I'm not too sure on the specifics but it works out for them and our guilds have made good progress in 25-mans.