We're getting a little off topic, but you can build the VNFS as a hybrid filesystem with "--hydrid --excludes-agressive=". This basically pulls all the non-essentials over NFS, we've been able to run X11 apps using warewulf with a 15-30MB ramdisk. If you have a half-decent setup you'll have different network adapters for NFS and MPI so the two don't step on each other's toes. As long as the program doesn't need to keep reloading libs (Gaussian for example is a pain for this reason), it works very well.
Also, if NFS solution isn't attractive you can add a few lines in rc.local to copy frequently used libs to a local partition on startup.