I saw a link about controlling Lightroom with a MIDI controller a while back. I have finally got round to trying it myself.
The controller was second hand from fleabay and the software (Knobroom) is free. I am using a Novation Nocturn. All powered from USB and has groovy flashy lights and dials. The software is pretty simple to set up and all instructions are on the Knobroom site. The mapping software pretty much sorts out the dials for you but you can customise them to what you want as well. It works well with Lightroom 5. UPDATE: this also also works with Lightroom 6.
Only got it yesterday but with practice and some setting up before I can see it speeding things up on the old LR front.
A few pics of it.
Size comparison to a MacbookPro 13 Retina
I have labelled the controller till I get used to all the dials.
Pretty much all essential sliders in the develop module can be controlled
I'm thinking of pairing this with my Wacom tablet to see if that will speed things up even more.
It's pretty groovy.