I wash all my down comforters (we have 7 total) once a month to once ever 2 months (if I'm feeling lazy). They just go into the wash individually... and then tennisballs in the dryer.
The most important thing is getting them *completely* dry. The tennisballs knock the feathers around and keep them from clumping and so they dry in about half the time (about 10 hours for a queen size, 7 for a twin). Trick. When you THINK it's completely dry let it go for about 2 more hours. Also... each time it cycles through, pull it out and stuff it back in. That way anything that got folded over doesn't stay that way keeping one small area damp.
It SOUNDS labor intensive... but really... it just means that you can't wash anything else that day, and once every couple hours you have to spend 45 seconds twisting a knob and stuffing it back in in a different angle.