I have given blood and rode home (3-4 mi).
1) Do not do it the first time you give blood.
2) Make sure you have no appointments after, as you may need an hour or two to recover.
3) If there is no mass transportation, bring cash for a car service just in case.
The biggest problem I can see (I have no medical backround) is that if you were in an auto accident and lost blood you would be in real trouble.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.