I recently acquired one thinking it was going to be a cool and useful feature, and the only time I think to use it is when I brush away a loose cat hair and my cursor goes all over the place. And the tablet mode, I think I used it once as a novelty.
Sometimes it's faster than finding the mouse cursor when clicking a link or a button (and when filling in forms with check boxes), but probably my biggest use is if I'm browsing around Google maps or Earth.
Click-drag click-drag on the trackpad is just slow and frustrating compared to just dragging the on-screen image.
I use a macbook sometimes and it's a bit infuriating when I try to drag the screen.
I don't use it constantly but I'm used to having the choice whenever I decide it's easier.