Add me to your list of those who think exercise during treatment (to a certain extent) and for sure after treatment aids in recovery.
I walked during treatment on almost a daily basis. If it was nice outside, that's where I went. If it was not nice, the cancer center had wonderful skywalks. Now at home I have an elliptical, which I use for 10-15 minutes twice a day. Not what I used to do, but I am only a little over two months out of treatment. Combined with housework and then I am back mostly full time at school I am moderately active. I am probably crazy for being back on the job, but I do think it gets my mind off of myself. Then, too, summer is coming, and school is ending in 3 weeks. I have lots of aches and pains about my shoulder, face, head, that come and go, but after I exercise I always feel better that way too.

I thought all those exercises we were given for recovery from neck disection and radiation were basically stretching exercises . . . and were good for you. They told me the first year was the most important year to do them, but probably really meant, "don't skip the first year thinking you'll catch up later."

Like Cheryl, I did not do much exercise my last week of radiation/chemo nor did I the first two weeks following. I think we can be excused from missing during that time.
Anne