Yes there are rumors that Windows 8 will offer better support for dual or multiple monitor Windows computers. There are rumors that Windows 8 will provide taskbar on secondary monitor(s) as well apart from that on primary monitor. Windows 7 did offered better support for developers of 3rd party software and provided ways to clone or extend connected monitors. It seems like Microsoft is finally trying to listen to what dual or multi monitor users have to say.
With increased processor speed, increased RAM, connecting an extra monitor might not affect a computer’s performance. Graphics cards do offer additional RAM for driving the non primary monitors and they do provide basic or sophisticated enhanced graphics capabilities. For personal usages dual monitors can be enough providing the facility of secondary monitor, which greatly enhances the available desktop area and the additional graphics card might support better resolution than primary monitor. Windows does allows switching of primary monitor to any of the monitors connected and hence Windows already provides fine control over dual or multiple monitors connected to a windows computer.
Windows 7 gave developers more ways to provide more functionality to users of dual or multiple monitor windows computer & now it seems like Windows 8 will provide some enhanced features as well for dual or multiple monitor windows users. In case Windows 8 provides an extended taskbar on other connected monitors, then it can be really useful & using dual monitors on Windows 8 will gain more popularity and of-course users of Windows 7, XP, etc might think of upgrading their operating systems as well.