Recently I have been looking at a series of papers detailing some hydrodynamic simulations performed by a research group in Australia (incidentally they are using a modification of a hydro code called VH-1 originally written by John Blondin at NC State University, just down the road from me. Think U of U and BYU, complete with similar colors, only BYU has dark blue and UNC has light blue. Anyway back to my post...). In their second paper the group finds "that the ability of the cloud to radiate heat is crucial for its survival", and that a non-uniform cloud will survive longer than a uniform cloud when hit by an expanding shockwave.
Now for a brief rundown of their research: After combining the hydro code VH-1 with a thermal cooling code called MAPPINGS III they ran their simulations of uniform spherical clouds and non-uniform fractal clouds. They introduced a shockwave that would accelerate and fragment the cloud (the shockwave would come from a supernova or an AGN). The motivation was to find out how filamentary structures are formed as observed in the center of galaxies such as NGC 3079 (picture credit to my adviser):
If you had asked most people to predict which cloud would last longer, the dense, spherical cloud or the sparse, non-uniform cloud, most would probably say the denser cloud, but it turns out that the non-uniform cloud would last longer because of the non-intuitive concept of radiative cooling.