I've donated blood a bunch of times in my life so far and, oddly
   enough, this is EXACTLY one of the thoughts I'd have... usually
   at the point where the blood loss caused a sudden need for a 10
   cent cookie and concentrated OJ and associated minor brain fog.

   Worth it though. They screen for all SORTS of nasties, free of
   charge and it's a decent enough path to infect the world with
   "me-ness", especially if it ends up in someone's penis.