I've been reimbursed for meals both by payment for services rendered and by per diem. I think everybody likes the latter - you can hide in your hotel and eat sandwiches, or cook something actually healthy (if you have some sort of facilities for it), or have a big blowout dinner one night. Bonus if you can score a hotel with a happy hour that you can scrounge a full meal from. Also, you don't need to keep track of every frickin' receipt. The other advantage of a per diem is that it makes dining out a whole lot easier if you have a crowd - 1 person picks up the tab the first night, and someone else picks it up the next, so you don't have to give the waitstaff grief by separating out 8 separate checks.
So I was pretty psyched when I was working in an area with an exceptionally high per diem (we were following the GSA schedule) and found a hotel with an acceptable rate that also provided a free dinner to guests Monday through Thursday night.
I was bragging about my per diem bonanza to a financially-minded person, and he said, "that's great, but are you declaring that on your taxes?" Taxes? He meant the part of the per diem that went unspent on food and was therefore additional income. I am a generally law-abiding, tax-paying type person, but I never considered the unspent per diem to be taxable. Anybody run into this issue before?