I think the 'open note' syndrome for guitarists is part of why transposers are legitimate at times even for keyboards. We all know how certain licks and runs fall easily under the fingers, and sound a certain way, but it take prodigious chops to play those exact same licks and runs IDENTICALLY in keys that make you finger them completely differently.

I can pretty much guarantee that if Corea or Hancock played one of their barn-burners in a 1/2 tone higher or lower than it's usual key, you would NOT hear exactly the same licks and chops. But if those licks and chops ARE part of the signature sound of a particular song, and the singer, or horn player, etc. wants to do them in a different key, what are you to do? Ruin the song by trying to be 'purist', or let the show go on by using your transpose?

What is getting confused here, I think, is the difference between being facile in all keys (which you need to be... even if you can only play in C, a bridge that modulates all over the place is going to force you to play those keys anyway) and able to transpose charts by sight and be indistinguishable from not transposing at all. This latter one is a rare commodity. While it's true you'll seldom see a jazz guitarist using a capo, you'll also seldom see a jazz pianist play a standard, particularly a challenging, much modulating one, in a half step away from the book key (or aug4, or any of those keys that REALLY change your hand position) and be as comfortable. The nature of the guitar means that, as long as the aren't using open strings, transposing for them means doing EXACTLY the same thing a fret or two higher or lower.

Essentially, doing little more than a keyboardist hitting the transpose button. I somehow doubt that, if it were so utterly different going from one key to another on the guitar as it is for piano, you would see so many jazz guitarists eschewing the capo! They certainly don't seem to mind it once open notes come into play... So much for 'purism'!

In a situation where you are likely to get thrown the same song on multiple nights in different keys (I'm in a band where they like to do Ipanema in F AND in D on the same night, depending on whether the sax player or singer is doing it... heck, sometimes he does BOTH at the same time and you have to modulate ), or a singer's voice is off and wants it down a half or whole step, when you are sight reading charts and the singer needs a different key, sure, I don't mind admitting I'll use a transposer.

But bottom line is, should I be stuck on a piano or organ without the transposer, I can still get by. I won't sound as good, and I might clam from time to time, but I can do it.

And, less the purists think the transposer evil incarnate, let us not forget that it provides the perfect opportunity to practice other keys for familiar tunes on the gig WITHOUT messing with the singer..! Just play them in a weird key, and transpose it to the right one!

Any sword cuts both ways...