Good man. It's a harrowing experience, but a good one in the end! My bother's been a regular blood donor since high school and I've always felt bad not for trying it. I'm not a squeamish person so I wasn't too nervous about my first time.
The injections stung like heck but didn't last for long. I was going strong for most of the donation but I fell ill near the end. Cold sweats, lightheadedness, numbness all over, cramps -- I never felt like fainting, but I was really out of it for about an hour. Probably a combination of being an unfamiliar shock to my system and me not eating enough that day. Fortunately I was back to normal by the evening.
I'd like to donate again in the future. I'll be on my new campus when my eight weeks are up, so I'll be on the lookout for donation opportunities.