Just testing that site (thanks to maxucho for providing the example :) ). Interestingly, even if I hold my mouse button down for a second or two before releasing it, there's still a perceptible loading time of maybe 500ms - 1s.
Not sure if that's expected as part of the design?
Hmm that could be just an issue on my site, not necessarily with the plugin. I've been experiencing some strange load times with it even before using InstantClick.
I set the preload to occur on mousedown rather than mousover, as per the docs, but even with this I noticed near-instantaneous page loading.