Just too darn much to leave on the lawn, guys. One year I never had a chance to get them up, and it messed up the yard bad. It might not have been quite as bad if I had got at them with a mulching blade on the mower, but this is mounds that are for the most part on a quarter acre or less of our grass; a couple of times I have lucked out, and the wind has come up enough in the right direction to clear most of them out for me. I'll survive, but it gets...interesting...
I have a lawn sweeper to tow with the lawn tractor/mower, but I can't count on getting once around the lawn without it being jammed full, so that takes forever too.