Thanks to the combined work of Torben Hohn, Kjetil Mattheusen, Paul Davis and a few other developers, it is possible to use Windows VST plugins (that is, plugins in VST format built and distributed for the Windows platforms) on Ardour running on Linux. (Note: there is no VST support of any kind on OS X).
However, doing so has three substantial downsides:
The dependence on Wine makes it almost impossible for the Ardour project to support this feature. Wine's functionality generally improves over time, but any given release of Wine may behave worse with some or all Windows VST plugins. It may even just crash Ardour completely.
Step back and think about what "using Windows VSTs" really means: taking bits of software written with only one idea in mind - running on the Windows platform - and then trying to use them on an entirely different platform. It is a bit of a miracle (largely thanks to the incredible work done by the Wine project) that it works at all. But is this the basis of a stable, reliable DAW for a non-Windows platform? Getting Ardour on Linux to pretend that its really a Windows application running on Windows?
We understand that there are many outstanding plugins available as Windows VSTs and that in many cases, no equivalent is available for Ardour's Linux-based users. If your workflow is so dependent on those plugins, then remain on Windows (or potentially consider using an actual Windows VST host running inside of Wine). If you can make the effort, you will get a better environment by using a normal build of Ardour and exploring the world of plugins built to run on Linux natively. This covers LADSPA, LV2 and Linux VST formats, and even some outstanding proprietary plugins such as those from LinuxDSP and Loomer.