On one of my sites, I have ranked number one for a couple of years on a certain keyword phrase because of something I originated and made. Let's call it a "size chart" for an example. (It's not really a chart, but I couldn't think of anything else to use for an example. It is something in the field of reference.) Six or so months ago, my "chart" disappeared from the serps. No matter what I did, the chart would not appear back in the serps. About 1000 people copied this reference chart and had it on their sites. They were ranking and I wasn't. I thought that Google maybe blackballed that page because they thought I copied it. So I forgot about it and went on to other things. Two weeks ago, I tried something just for the heck of it. I put the chart page into addmefast for some plusses. I sat at the computer and watched the points go down by constantly clicking refresh. I stopped the plusses when about ten people plussed the page. I did this every day for a week. This morning I checked and the chart page was back in the serps for that same keyword phrase that has been gone from the serps for six months. It could not have been anything else but Google + because that's the only thing I did.