I like to think I know a little about this too
I was a participant in one of the big international scientific trials of this vaccine before it was released on the market. This meant that I got either placebo or the vaccine three times over the course of six months (like someone explained here), and then was tested for HPV and had a pap smear several times a year for over 3 years. Turns out I did get the placebo, though, but was offered the vaccine for free after the study was over. Anyway, I ended up not having it, because I was nearly 25 and was told by the docs administering it that it probably wouldn't make a difference for me. Still, it wouldn't hurt, as they said.
On a side note, I did have cell changes on several occasions, despite the fact that I didn't get HPV. The changes turned out to be benign, and they also changed back to normal on their own after a while. The gyno said they probably would have never been discovered if it wasn't for me participating in the study and getting tested so often.
I guess the moral of my story is this: don't panic either way, you probably will be fine without the shots, but they probably won't hurt either. Everyone should have pap smears regularly, but even if they do find cell changes, they could be totally benign and go away on their own.