Taking a look at this article from 2005, fig. 8 shows that liquid jet-impingement definitely has the highest heat removal capability. I guess IBM's come up with a way of sealing that chamber around the chips, filling it with a non-conudctive liquid (the article gives the example of fluorocarbon), & fitting the whole she-bang inside a server chassis... crazy.

"Full details of the technique, which Bruno Michel, manager of the advanced thermal packaging group at the IBM Laboratories, says is one of the most promising that the group is researching, are due to be given at the ITherma conference next week in San Diego, California."