Interesting discussion. I always bag to the limit of my system, which is 17 in of Hg. I don't use real breather cloth any more; for the layups I am doing, paper towels generally get the job done. The key is in how you apply the epoxy. Typically my layup schedule is so dry to begin with-I wet-out cloth, bag with paper towels to remove excess, then proceed with the rest of the layup, place peel ply and 2 layers of paper towels down. The key is not removing too much epoxy from carbon, which is tough as carbon looks nearly the same wet or dry. Another issue is saturating the foam/plywood in the layup, which you really don't want as that is just adding weight without adding strength. Higher density foams (I'm using Rohacell IGF31, for boat work IG 71 is the ticket) aide in this.

Of course, I'm working on such razor thin margins that West Systems is useless to me, as the viscosity is too high. I prefer Resin Research Composite Pro Systems, as it is less expensive, has equal or better material properties, and has lower viscosity. For really weight critical applications, I'm using Pro-Set or MGS. http://www.rcgroups.com/forums/showthread.php?t=1546707