I'm O positive - that's pretty close. Since negative is rather rare, my blood fits over 80% of the population. If you're A-negative and get in a car accident, I can't help you.
Also - I donated platelets. Blood type doesn't matter for that. Takes two hours, so you get to watch a movie. It's hard to read a book, because they stick both arms (they extract your blood from one arm, spin out the platelets, and give you back your refrigerated blood. It's wicked cool.)