For my last site, I decided to purposely do an experiment and build a whole bunch of links, and then just leave it.... After a while of my links getting recognised, I started to rank well for a while, then the rankings started to drift and drift off they did until I was down to below page 7.
Now for all of my links, I ran them through Scrapebox and they are all still there... So no problem with the links.
The fact this has happened a few times now leads me to believe that link velocity is a major spam buster in the Google algo, and its a smart one! As a lot of people here state, Google can't really penalise you for building backlinks too fast, however it will take into account your linking velocity, so unless in that initial surge of links you have say 10 or 20 x your competitiors link, the link velocity factor will start to see your rankings drop!
So beware, if you intend to have a major linking campaign going forwards, you need to keep the link quantity up... Once you are top you can probably slow things down if you wanted to (I wouldnt, I would keep going to distance myself further), however it would be best to do so in a tapered manner.
Numerous experiences counts volumes, so beware.
Anyone else with any personal experiences of this at all?