Let’s put this one in the “it’s there, but not really useful…. yet” category.
Novato Music Press via www.freehandmusic.com is publishing sheet music in Amazon’s Kindle store. What does this mean for gadget people? Not much. Amazon’s Kindle has a 6″ diagonal screen and the Kindle DX has a 9.7 inch screen. Their sheet music has a large border, about 1″, so the actually viewing space on the Kindle is limited. Even on the larger Kindle DX the printed music is limited to around 7″ diagonal. Amazon has produced an iPad app that allows access to the same Kindle content; this app lets you zoom in, but the music is still too small. The music needs to be larger and the music reformatted in order for this to be a viable resources.
There are, currently, a handful of trombone works available on the Kindle store – pieces that are out of copyright protection. They are very cheap: $1.00-$4.00, but they are really only good for novelty or for study on the go; these are not useful for practicing. Yet.
As screen resolutions improve and Amazon expands to more and more devices, this may prove a viable resource.
Screen shot of Gardell Simons’ Atlantic Zephyrs from the iPad:
University of Iowa Trombone Studio 
Check out the air turn, it allows you to turn pages with a foot pedal. Dr. Huckleberry has one.
http://airturn.com/
It looks like a good resource. My issue with the Kindle sheet music is that it is too small at this point. A fancy page turner (which I want!) still won’t fix this issue.