I think the most likely side effect you may have is a sore arm. Vaccines really kick my upper arm's ass, all the time. Gardasil. Flu. I'm sure any other vaccine I get in the future will leave my arm in pain as well :P

OP-have you ever googled a birth control method? You'll find many, many horror stories for any of them, some true, some not. But the you're going to find much more people turning up to voice complaints than they are positives.