Giving blood and training/racing

I wouldn't personally.

Last month when I donated, it took me almost a week to a week and an half to feel "normal". I raced my first Du after nine days, although I did notice a good difference in performance. However, I did go to cross-country practice the next morning, just took it easy, but I'm not always the most intelligent.

There will always be another donor clinic somewhere. Try the website for company that organizes it in the US.

I wouldn't do it either, especially since you're doing long runs this weekend.

There is always a shortage of blood and blood products around holidays.  After Thanksgiving or around Christmas is a good time to give blood.

Hate to be contrary, but there's no real significant variation among people in how they "recover" from donating blood.  If a certain amount of blood is taken away, each person will regenerate those red blood cells at a pretty standard rate.  Regardless of feeling ok or not, there is a difference in those who've just donated and those who haven't.