Clearly, Canonical can't do anything right.
Oh, and also, Mint has had a huge rise in popularity at the same time, and, by the way, the graph shown in the article, in addition to any methodological flaws it may have, only shows relative numbers; Ubuntu drops from 11% down to something like 4%, but of what total? We have no idea from this graph whether there is an absolute drop or rise in the number of Ubuntu installs; only that Mint has taken off, relative to other distributions.
There's nothing in the data shown that ties this to Unity specifically, or even anything about Ubuntu itself. There have been hundreds of changes between 11.04 and 11.10, and the Linux landscape itself is changing at the same time. I don't see any firm data presented to blame the UI.