Nice extension!
I installed it and in Vista 64 the custom columns work fine but the Thumbnails do not show. I had to open a 32bit version of Windows Explorer to see the thumbnails of the Kindle books.
Forgot to add: Avira seems to think a tmp file in the MSI setup is a trojan. I had to disable it to let it install. I thought you might want to know. It's obviously a false positive but other Antivirus programs might think so too.