This cable is the cheap solution to get ati eyefinity (3+ or multiple displays running the same game/program). I was concerned at first when i saw other active converters for £80+ that had usb power, however, this has no USB power connector, it is a fraction of the price and it works fine.
Bought the new ati radeon 6870 which has 2 mini displayports (DP) rather than full sized DP, connected this cable between a DVI cable and the DP/mini-DP cable that came with the card. Works fine, got 3monitors running in no time.