When I got this years flu shot, my arm started hurting right after getting the shot and then it was very sore for about 4 hours or so. Luckily this went away. A co-worker said that she didn't feel sore at all.

Several years ago my arm became so sore that I could barely lift it up and use it for several days. I called the advice nurse and she hadn't heard of anyone having this kind of reaction. Later on I learned that my roommate had also had the same kind of reaction. I'd still rather get the flu shot than to risk getting the flu though.