I asked my surgeon, who said that risk was low, and it was very rare that he had needed to use blood. He basically said knock yourself out if you want to, so I did go to the blood bank that works with the hospital where I was to have surgery.
I filled out the forms, and their faces went white as a sheet when they reviewed them. Seems that my several years of living in / travelling to areas in the UK where mad cow was rampant disqualifies me forever from even walking into a blood bank, much less having any drawn.
I mentioned that to my surgeon later. He smiled, and reminded me that the practice does a very thorough history document, and he knew what I would find at the blood bank.
When I reviewed the hospital bill, I found that they had prepped and on standby two units, although they were not used. Aflac did pay a per-unit amount for the fact that the blood was on standby.
So maybe not to worry?