@Protomartyr nice poll - question to discuss
A vertical position of the taskbar makes sense because most screens on PC's are wide screen landscape, so having the taskbar on the left or the right leaves more pixels for content.
On a tablet or mobile phone a top or bottom position of taskbar makes more sense because tablets and phones are most used in portrait position.
Most apps have most used tasks/icons oriented on the left (a natural result of western languages written from left to right and top to bottom). So from a mouse distant perspective the left vertical position makes most sense.
Since most application taskbar's are at the top, it would make more sense to put the desktop taskbar at the top also. Why is it that most desktop GUI-designers put their taskbar at the bottom? The reason is structure and task separation. Most people find information easier when they are not placed adjoining but with spacing. So from a human information interpretation point of view the best position is on the right.
User behavioral tests have also shown that bottom-horizontal position taskbar users adopted the right vertical position easier than a top-horizontal or left-vertical position.