Are there any dual monitor adapters for the Mini Display port that support true multi monitor mode? For example the Matrox Dual Head To Go just makes your computer think it's connected to a 3360x1050 display rather than 2 1680*1080 displays and you have to do lots of work arounds to ensure that the dock doesn't span both monitors and alerts don't show in the middle of the monitors etc.
In theory Displayport 1.2 supports daisy-chaining and hubs, which would support this, provided you have a Mac that supports Displayport 1.2 (I think it's just 2011 Macs and later, but I couldn't find a definitive answer). However as far as I can tell, there aren't any monitors that support daisy-chaining available, nor are there any hubs expected until sometime in 2013.
At the moment you're restricted to the adapters that concatenate the two displays, rather than present them independently. An alternative might be a Displaylink adapter, which allows you to connect a monitor via USB. It does limit performance however, but how much this impacts you depends on what you're using it for.
DisplayLink is not an option if you're using a VM (e.g., Parallels) with Windows. Attempting to intall Windows drivers for DisplayLink USB adapters corrupts the Windows installation, requires rebuild of VM content. Hidden 'way down in Diamond web site is a warning that drivers do not install in virtual machines. J5 Create adapters do work, however.