It peaked at 4.05% in March. The last 2 months it went just below 4% as the Unknown category increased. For June the reverse happened, so 4.04% seems to be the real current share of Linux on Desktop as desktop clients were read properly/werent spoofed.
I have some Sandy Bridge systems here running strong as Linux desktops for light work. You know, these 4-core 3,3GHz processors from - hmm - 2014?