I've used a right-side taskbar since Windows XP, so yeah I've been feeling pretty angry about this.
I experimented with all four sides. When I last used it on the bottom I often had it "huge" (three or four rows) with auto-hide because I didn't want to cramp vertical space that much. I thought left and top got too much in the way of Fitt's Law related muscle memory. (More applications have important controls like menus to the top and left, and when maximized you are used to just rushing the mouse to the screen corner to access them, having to back across the taskbar never quite worked for me.)
Right-hand side seemed optimal to me in Windows XP and continues to feel that way today, especially as monitors have only gotten wider from when I started on classic square CRTs.
Since Vista introduced "Aero Peek" I felt far less of a need for window titles directly in the Taskbar, so I generally only ever use the Taskbar about the same width as the default height when at the bottom. (I like it just a tiny bit wider than that where on the main monitor in a vertical orientation Windows expands out the full date and day of the week in the clock panel.) At those widths my right side taskbars take up far fewer total pixels (and especially far fewer total unused "whitespace" pixels) on widescreen than a horizontal taskbar. It's especially a stark contrast on my ultrawidescreen home desktop where you just lose so much valuable screen real estate to wide empty expanses of taskbar when horizontal.
(I even appreciate the thought/theory behind the centering they are going for bringing things better into "eye line" on an ultrawide, but with all those wasted pixels around it I could be using to uncramp vertical space in apps, I think they have the right general idea but the very wrong implementation.)