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.
In my experience, experience with one distro is experience with them all. 90% of what you are familiar with will be either similar or completely the same. So definitely give LMDE a shot.