Well, this should embarrass the heck out of Spotify. If Spotify's software developers aren't embarrassed at all, then clearly they're all mentally unstable. Seriously, I know modern proprietary software tends to suck, but I can't imagine how this happened without someone noticing something before the software was released.
10 Gigs per hour is about what I would expect from a Windows 7 installation (the last time I installed Windows 7, it took about and hour and a half, so that's actually pretty close). Assuming the data isn't auto-deleted, this could easily screw with HDD users, too, since they only have so much disk space to spare.