depends on the position. For lineman it's almost completely irrelevant, LB'ers barely relevant...but for positions like WR, RB, DB...those guys stretch their legs for at least 40 yds on nearly every play during a game. I would like to see the guys at the combine have to run multiple 40's with enough time in between that you get in a real game. Let's see these guys run 4 or 5 back to back 4.3's. Ain't gonna happen.
I'd also like to see them toss the 225 bench...that's the most meaningless metric of all. Have them bull rush a 340lb sled, see who does it the fastest.