I've had the same problem -- both in background install mode, and foreground install mode it actually seems that this might be "normal". After force quitting the background installer after ~20 minutes of CPU time were used, I ran it in the normal double-click mode. After getting through most of the way through the install, it pegged my CPU. The progress says "Search In C:\Program Files\Inkscape\etc\fonts\conf.avail". I'm guessing that this is just some sort of font scan that eats up absurd amounts of CPU time.
I've had the same problem -- both in background install mode, and foreground install mode it actually seems that this might be "normal". After force quitting the background installer after ~20 minutes of CPU time were used, I ran it in the normal double-click mode. After getting through most of the way through the install, it pegged my CPU. The progress says "Search In C:\Program Files\Inkscape\ etc\fonts\ conf.avail" . I'm guessing that this is just some sort of font scan that eats up absurd amounts of CPU time.