I got a new system, and in trying to get the Radeon HD 5450 to output to 3 monitors at once, I booted to an old install of Linux Mint. After updating, and far too much fiddling with drivers and kernels, and rebooting, I got it to work, albeit not consistently. I decided to switch to Mint from Ubuntu on my main install, hoping that I would have better luck with a fresh install than I did with an incorrectly updated system. Unfortunately that was not the case, and so until I either buy a second video card, or replace this one with a card that has Display Port output, I am stuck with 2 monitors. Poor me!
I installed Mint 17.1 Rebecca Cinnamon edition, and after install added Mate, and KDE (gnome has install conflict that I haven't looked in to). Booting in to KDE works perfectly, except that my dual-head setup defaulted to both of my monitors being cloned (or perhaps overlaid, although they have matching resolutions so I can't tell which), and no obvious way to change it. I installed KDE using the kde-full meta-package, so I expect all of the available functionality to be there, but when I looked in the settings under "Display and Monitor", all I saw were "Screen Locker" and "Gamma".
A quick search led me to a package that for some reason isn't included in kde-full. It's called "kscreen", and while I think its exclusion is an oversight, I have to give them full marks for execution, because I didn't have to do anything to enable it. Want to install it in Mint? Here's the command:
sudo apt-get install kscreen
Before Synaptic package manager had even returned to the package listing after the kscreen install, my monitors blanked and came back with the extended desktop I wanted. Kudos!
Is having a multi-monitor setup rare? Let me know in the comments whether you have 1 or more monitors.