Paul sez: Someone asked about getting a shorter-scale guitar as a response to
problems with playing.  Here's what I responded:
in about 1994 after playing guitar for decades, I had to stop for almost a 
year when I got RSI.  So I've been all about the ergonomics of my guitars 
ever since.  I now practice every day and play a weekly gig in church, so 
recovery was possible, although it took a long time.

Yes, a shorter scale definitely make things easier. An inexpensive 
alternative to a different instrument is simply to regularly use a capo to 
shorten the scale of the guitar you already have.   When I was recovering, 
I started tuning my guitars down a whole step for reduced string tension, 
and I would then capo up two frets to get back to concert pitch.  In 
effect, this turned my standard dreadnought guitar into a shorter-scale, 
12-fret guitar.  Capoing often lowers your action a bit too.

(Once I started playing in a church band I discovered that this detuning 
also makes it easier to play songs that are in keys like F or Bb since you 
can just pull off the capo and be in a friendlier guitar key!  I got one 
of those Slider capos for my acoustic that stays on the guitar all the 
time: playing with the full scale of the neck is now the exception instead 
of the rule for me.)

Although I've recovered, I still detune my electric (10 - 45 strings)  and 
steel-string acoustic guitar (12 - 54 strings) by a whole step: I just 
like getting the lower range, along with the looser strings.

That's not to say a new instrument isn't a good idea.  My steel acoustic 
is a big box and if I have to play a lot, the right-hand reach around 
starts to hurt my shoulder and neck.  I've often considered a thinner body 
acoustic, or a roundback, or even one of those Variax acoustic-electrics. 
There are some nice 3/4 size guitars out there that also feel comfortable.

I keep my classical guitar, with the softer nylon strings, at concert 
pitch, BUT up until a couple years ago I was getting ready to trade it off 
because, with the action set high enough to avoid buzzing, the string 
tension and wide neck would begin to provoke my old injury if I played for 
more than a couple of minutes.  My saintly guitar technician objected to 
my trading it in and insisted on adjusting the action and low and behold, 
it was much easier to play and no buzzing.  Now I play it all the time.

Likewise, when he refretted my worn-out steel string, when I first tried 
it out after the repair, it seemed like it was just somehow more stressful 
to play.  He grabbed his wrench and made a small adjustment to lower the 
action just a hair's breadth, and suddenly it felt great. 

So the moral is, work with your tech to find the right strings and 
tunings, and make sure he sets the nut and action as low as practical* to 
avoid unnecessary extra effort.  And try the capo as a regular part of 
your instrument. 

*consistent with YOUR playing style.  Part of my recovery was learning to 
play with minimal effort and I don't go after it like Ani DiFranco in any 
case.  But even very aggressive players sometimes find they can get the 
job done with less string and muscle tension.

UPDATE: thanks to an extravagent birthday gift from my mother, I addressed some of the issues
of my big dreadnaught by purchasing a Martin 000X1AE guitar.  With a smaller, shallower body, 
it has been a huge help with the strain on my right arm.  An impeccable neck makes a really 
easy action a reality, and even the inexpensive Sonitone pickup option lets me play quietly
and let the amp do the work.  And because of the composite materials, it is very 
inexpensive - about $500 -  and above all, it sounds just great.  So an ergonomic 
instrument doesn't have to break your budget.

There's more info about musicians and injuries at my website here: 
http://rsi.unl.edu/music.html .