Thanks Eric--this is great!  Using dynamic_reconfigure with the Logitech 
9000, I see the expected effect with all parameters except exposure 
which generates the error:

setting control 9a0901
current value of 9a0901 is 3
unable to set control
: Input/output error
[ERROR] [1292729915.173487152]: Problem setting exposure. Exception was 
unable to set control

but setting absolute exposure works fine so no problem there.  The one 
glitch I ran into was in setting the width and/or height in 
dynamic_reconfigure; because you can only set one at a time, as soon as 
one is set, uvc_cam warns:

[ WARN] [1292730153.471431256]: Reconfigure callback failed with 
exception pixel format unavailable:

and then image_view freezes.  If you then continue to set the other 
dimension in dynamic_reconfigure, it does not unfreeze the image. 
Restarting the uvc_cam node *does* unfreeze image_view and picks up the 
new resolution, as long as you don't have width and height hard coded in 
the launch file.

Will test more tomorrow.

--patrick