Good news for anyone (read: both of us) who have had to wrassle Calibre and it's many dependencies to get it working:
I noticed on my PPC debian box that the .deb of Calibre has been updated to 0.8.28.
You have to be running Wheezy and have everything apt-get updated/upgraded to the moment. Otherwise it'll sit there and tell you that it won't install the dependencies, etc.
I'll try it on my pogoplug debian setup tonight, but this looks really promising.