> I was told over the weekend by my uncle, who is a nurse, that the official American Red Cross recommendation is that you shouldn't give blood or any portion thereof -- plasma, platelets, whatever -- more often than every 54 days and that doing so can cause some pretty screwy problems. Can anyone confirm or deny?

Well, over here the official line is you have to wait 16 weeks, although that recently dropped to 12, I believe, because of shortages. So that's 84 days in the UK.