Set over set is a pretty small worry. Should not be part of your preflop odds-calling decision. If you're even getting 5-1 PF, it should usually be a call as you'll make up a fair amount after the flop. Does anything pay off much better than a set? You certainly don't need 8:1 to make a call good.

Further along, that 40% chance that 2 players have a pair PF -- is that flat odds? or is that the odds that if YOU have a pair, another player at a full table will?

I know it doesn't consider the fact that there are all those cold-callers. That's gotta make that 40% figure faintly rediculous for any sort of odds discussion. Not that it isn't a good rule of thumb...