Somebody on amazon, wrote the following about passive adapters (http://www.amazon.com/Accell-B087B-001B-UltraAV-DisplayPort-Adapter/dp/B001CXXD2Q/ref=pd_cp_e_3):
I bought this to run 3 monitors on an ATI 5770. I thought I could use this because it says right on the package "Active Technology" and I knew that passive adapters won't work for three monitors. Yes, this will work if you want to run two monitors but in order for the ATI 5770 to be able to output to 3 monitors, one must be NATIVE DisplayPort and an active adapter is required to convert that signal to DVI... but even though this claims "Active Technology" and that it has built-in circuitry and "Features a Self-Powered Design" it DOESN'T WORK TO RUN 3 MONITORS! Check ATI's site for "ATI Eyefinity Validated Dongles".
Additional info: It seems the 5000 series cards have two RAMDACs so they can only output two signals that require a RAMDAC. A native DisplayPort signal does not require a RAMDAC. Because of the two RAMDAC limitation, the only way to get three monitors is to use a native DisplayPort signal because it doesn't require a RAMDAC. Passive converters DO NOT convert native DisplayPort signals and THEREFORE REQUIRE the use of a RAMDAC. Because only 2 RAMDACs are available, a passive adapter, which requires another RAMDAC, won't work for 3 monitor setups.
So I wouldn't waste my money in a passive adapter if you really want to connect 3 screens...