Good Question!
Searching will find examples, but here's a summary:
Many people have found that removing the shroud and screwing two 80mm fans on reduces the temperature (one will overhang, but nevermind that).
Some people swear by using two 60mm fans which fit directly onto it (after removing the shroud).
Replacing the stock fan (which isn't particularly powerful) with something with a little more grunt will undoubtably increase airflow and reduce temperatures. However, take care not to have too much pressure going through the VGA silencer as it will actually reduce the performance of the unit (think blowing air through a straw).
People are also having success using a blower with the VGA silencer HS and shroud.
Me? Mine's unmodded. My overclock doesn't change whether the silencer is on low or high, so I doubt my core overclock is limited by heat. It's an R360 core on a 9800 pro, so I guess I got screwed (maxes out ~440core).