Pouring cold water on pasta after cooking it
I would strongly suggest not pouring cold or any other kind of water on pasta; it will rinse the delicious starches off its surface, which would otherwise help your sauce cling to it.

To counteract the negative consequences of overcooking due to remaining heat (which, as belisarius suggests in his answer, is the reason other stuff is often rinsed with cold water), just serve it immediately. You want to have the sauce (hot and) ready just before your pasta is, so you can drain the pasta, mix with the sauce, and put it on the table.