I've been meaning to put this out for discussion for a while but never remembered to do it when on line.
I've watched the 20 second clock for a few years (when I think about it) and, other than for the purpose of killing time, most plays get off in 10-15 seconds. I'm all for the idea of reducing the 20 second clock to 15 seconds. This might add only a few plays to the average game but most of those plays would be in the final minutes.
I think 20 seconds is fine. What isn't fine is 40 seconds in the NFL. They should change this, the game comes across way too slow for the top notch calibre players they have down there, doesn't do them justice. And a few other rules I'd like to change down there too to make it more exciting and fast like the CFL. Can you imagine qb's like Vick with 20 sec clock and 3 downs where he would make some more runs from time to time with the 1 less down! Man, that would be awesome, as well as seeing more of their punt returners returning more punts. Oh well, never going to happen I guess.
If the TV would show the 20 second clock on a regular basis I think you would find that most plays are executed between the 15 and the 20 second mark.
Also, I believe that the QB has a very complicated job, if you rush him, you will see more QB errors, confusion by all, and poorly executed plays. As it stands now, the players have just the right amount of time to get to the line, have some motion, and to actually 'think' about what they are supposed to do on the upcoming play. It is that 'thinking' that adds to the quality of an offensive play. And, after all, isn't it offence that the fans come to see - a player that puts thought into the upcoming play will likely execute a well thought out play. So the choice is: quality play or rushed play with little thought...
The big problem I have with the NFL 40 second clock is that combined with 4 downs, it is too easy to protect a lead. As a result, successful comebacks for wins are extremely rare in the NFL compared to just about any other sport.
I've actually got a new idea for an effective mix (Kanga you'll like this) between rugby and gridiron. It works best when you use a CFL and NRL basis (as opposed to NFL and IRB), but there will still be 4 downs (you have to make between 10 and 15 yards per set of downs). I'm not instituting a play clock, but instead one referee will count off from 15 after the ball is downed (and aloud at 5). If the game ends up too slow, 12 or 10 second counts will occur.
Anyways, to get back to the topic at hand, I think 20 is good, when I watch CFL I don't see an intense speed rush in the game, but when I watch NFL I'm bored. Maybe that's the inherent difference.