Most sw developers, and quite a lot of other people runs multiple monitors.

And the CAD guys have been doing it for a huge number of years.

No special drivers needed. You normally get the option to either extend your desktop, so you can drag applications from one monitor to the next (and when you extend the desktop, you graphically arrange the two monitors so the computer knows if they are beside each other or if one is above the other) or if you want to clone the desktop so you have multiple monitors showing the same thing (for example your monitor and a projector for an audience).

Matrox have quad-headed boards so a single board can control four monitors. And as mentioned, you can install more than one graphics card - that is one of the reasons why you can find graphics cards with the PCI bus even if the world moved to AGP or PCI-E many years ago.

One thing to think about: There are some programs that are very stupid about multi-monitor setups. They may decide that "full screen" should cover all monitors. Or they may decide that any message boxes should pop up in the middle of the extended desktop, which may result in half the dialog on each monitor. The special drivers for your graphics card (at least for NVidia cards) often has special helper applications that can improve the situation. You may have a configuration that says that a dialog should always pop up on the same monitor as the main window, or on the same monitor as you currently have the mouse pointer.

In the majority of cases, it will work quite well, but a few programs thinks they are smart enough to handle multiple monitors themselves but does so in a totally broken way. One application I have always decides to go full-screen on the "other" monitor...