Well, actually just Sensei for a little over an hour. This past Thursday my Sensei had to deal with a semi-emergency, and I took over the children's class for the last 10 minutes, and all of the youth class. It went well - they're all used to me as Sensei's co-trainer. Our Shihan and Sensei's previous standard co-trainer, a brown belt, showed up during the youth class and helped out a bit with some questions. The brown belt then took over for the adult class.
Today (Saturday) I was guitarist for another Musical Fireside, this time an hour away in Korbach. It went quite well - I had an interesting chat, played a bit of background music, and at the end, there was a rousing round of "Amazing Grace" with DW and some others there who had choir experience.