Back in 2011 Google hit us with the Panda updates, then early in 2012 came the Penguin (April the 24th if I remember rightly) and since them there have been literally hundreds of changes and tweaks to how they are ranking pages, this in turn has been reflected in peoples websites jumping up and down the ranks like a mad thing all summer.
I have a personal website too, that site does compete for some pretty noncompetitive terms to be fair, but for a few weeks it held positions 1 through to 8 on page one then the entire of page 2 and 3 for several terms. While I was quite happy with this level of exposure, I could see it was never going to last, it doesn’t really give someone a choice when a single site dominates the ranks in this way.
There was another example of this happening with a clients site too, unfortunately it wasn’t his site which dominated, but the main vendor who he buys from. They had the first 8 spots on page one while he held position 9 and 10. His sales didn’t drop off though despite having been pushed so far down the page, as the vendor were significantly more expensive than him, so although they had to scroll further to find an alternative, the other re-sellers had all been pushed back to page 2, so it was just him and the vendor left on page one.
All that was great for a short time, but Google obviously needed to address this, which they did around a month later, but I do wonder how many seo companies lost clients when their ranks came tumbling down. Only to find a new company and see them rise straight back up again.