A couple of light years ago. Didn't fight, but trained and sparred with boxers/kick boxers to maintain fitness. Whilst I haven't been in a boxing gym in ages, I've still used a few of the training techniques like skipping, circuits and interval training over the years whenever my bad living has got too much and I feel the need to work on my cardio fitness levels again......currently in such a stage at the moment......who knows, now that I've given up the smokes, this time round I may even keep it up!! :-)
It's had no effect on my drumming per se, other than when I feel fit, I feel better. One concern I did used to have was hurting my wrists on a heavy bag though......I've always tried to keep them supple for drumming. Strapping them helps and whilst nothing ever came of it, it was certainly a worry I had in the back of my mind for some reason.