Because I think the best bench players know exactly what their team is missing by the time they are ready to enter the game and they're ready to provide it.

The active part goes without saying, the superior second unit guy is usually going up against tired starters or shaky bench units.  If he's got a lot of energy, he is typically going to make good things happen.  Assuming he's smart of course!

Versatility also needs little explanation.  It does no good to realize your team needs shooting if you can't shoot.  It does no good to realzie your team is getting pounded on the boards if you can't rebound.  

Manu Ginobili always comes to my mind as an ideal sixth guy, and he possesses all of the above traits.

It takes someone with a high enough basketball IQ to be able to pay attention to what is happening from a far and apply those needs correctly.  Really someone who excels under these conditions would probably make a great coach.  I do want to add one more thing that can be read as slightly more negative: It's a mental state in many cases.  In Jack's case he's not a true distributor and this makes off guard make more sense and since Roy won't be exiting the team Jack is the first guy off the bench if it's a guard who sits.  If Brandon is injured then Jack will be the starting SG.  Back to the mental state, whether Jack's conscious knows it or not he is not best suited to be a point guard, I know he really wants to be... that's were the mental hiccup comes in I think.  I think he relaxes more and doesn't feel the weight of the world when he is not trying to prove that he can be something that he may not be best suited for with regards to natural strengths and weaknesses.  I don't want to put too much of a negative spin on this, we all have our ideal self-images, and Jack's happens to be something that most think isn't what he's destined for, and whether it's those doubts creeping into his own conscious or subconscious or not he plays differently when he doesn't have that pressure.  What I think is ironic and could be documentation that it is a mental state (in many cases - Jack's in particular) over time is that I am willing to bet that Jack will play just fine in games that Roy is injured to the point that he doesn't play.  I think he'll bring it and deliver, but I think if he goes back to starting as a PG he won't nearly as consistently, that is partially due to natural abilities, but has just as much to do with Jack thinking too much about how he can be PG again.  A combo guard is an interesting thing because there are times that you can see that this person can play the point, but to me someone who is truly a point guard you can just tell in the way they play from the first time you see them, even when they are not ready yet (Sergio for example... definitely not a 2 when you are playing to his strengths), even if they never make it... you know it's PG or nothing.  To me Jack has never had that, I know he wants to be that person, and I think it's caused a mental situation that will doom him when he plays the 1, but he'll consistently shine when he doesn't feel more pressure to prove himself beyond just playing smart ball and scoring when it's an option, two things he's naturally great at.  He's very comfortable there.

and think of who has been sitting on the bench all season watching and learning.  (And I don't mean Raef or Darius.)  I hope he is talking with the coaches and asking about things and using his intelligence wisely.  Even though he is not contributing this year he may be learning a great deal that will help him/us when he actually gets on the court.  This season on the bench may pay dividends we hadn't expected.  

I think for the rest it depends on how they use the time.  (Even the starters when they are resting.)  Are they watching & analyzing or just watching like most of us in the stands?  We know that JJack and Roy both have pointed out things they've seen from the bench ... do Frye & Outlaw & the others watch with intelligence or just watch (or joke with the other bench riders)?

I've been pretty neutral abt JJ the last couple of years, but I really like where he is playing now. As long as he doesn't THINK about it too much, I really like him as the sixth man.  It's hard when everyone calls it a "demotion" - but if you can get your head around it (as Ginobili obviously has) it can be a more important role than being a starter.

Intelligence, which you all have covered here, and a lack of ego (or a commitment to winning that trancends ego).

Havlicek, Schrempf and Ginobili illustrate both.  They also spent a lot of time as starters.  Surprisingly, Artest does as well.  A lot of people do not give him enough credit for his intelligence.  The fact he does not always think before he acts does not mean he's stupid.  And while he does have a rather large ego, he's also shown that he wants to win very much.  For me it's more a matter of having a good coach, who knows what buttons to push and when, to keep Ron-Ron focused.

points are valid. A subtle but I think common thread among the very best of 6th men, is a certain reputation and mystique.

  At his best, Vinnie Johnson was perhaps much more feared by opponents as a 6th man, then he would of been if he had been a starter. As a 6th man, he gained the reputation and mystique of an asset that was going to come in a game, and would make a difference.

  I think the same can be said for Havilcek, Detlef and Ginobli. Great 6th men become more than just the first person off the bench, the best become an instant lift, and a headache for opposing teams.

  Jarrets having a decent run in his off the bench role, but I don't think he has reached this level of respect, talent and mystique.

I have to be away from the computer for a couple days. Very good points made. Keep it going.