A accurately as I can time it with a stop watch, it took 16 ± 0.5 seconds for the busy icon to disappear when launching Nautilus from the panel, the favourite list, the mint menu or an icon on the desktop. There is no delay using the Home icon on my desktop.
So thanks for the tip, but this must be a bug.
Desktop: Dell, Intel Core 2 Duo E7500 @ 2.93Ghz, 2GiB RAM, Linux Mint 13 Maya.
Net-book: SAMSUNG N148-Plus, 2x Intel Atom CPU N450 @1.66Ghz, 1GB RAM, lubuntu 12.04.