I use a MPD32 to control the OT, all the time. The pads are set up to trig tracks with different notes (e.g., kick base pitch, kick pitch +7…), start/stop recording on pickup machines and change patterns. As a side note, one bank of pads controls iMPC which I usually have running in the background and either provides audio to the pickup machines or runs in parallel. Additionally, a MPX8 for standard 909 snare, clap, hats, ride, crash and some vocals to be always quickly accessible!
For velocity-sensitive control that also makes use of aftertouch and records note lengths, I plug a Midi converter between OT and MPD32:
http://www.elektronauts.com/t/ot-midipal-drum-pad-great/7717