Sorry if this starts a new thread unecessarily, but I seem to have found a simple and fast solution to the problem that the Calibre manual mentions
here, namely that putting your Calibre library in a Dropbox folder on your computer can lead to complications. My solution, which I have not seen mentioned elsewhere, is to export the library to a separate folder, e.g. "Calibre Backup," and put that folder in the Dropbox folder. That will avoid the possible conflicts mentioned in the Calibre blog, and also (I think!) uses up relatively little space in Dropbox, as opposed to storing the whole library there. Of course it also means that you have to export your library to that Dropbox folder regularly, but this to me seems easier than getting the synchs between various copies of the library mixed up. When I had the main library itself in the Dropbox, it seemed fine until somehow I ended up with multiple copies of many files and don't even know how it happened. This way is straightforward and transparent and should work without complications -- but please let me know if I am missing something!
By the way, just in case someone has the patience to explain it, I do not understand exactly what "Use the previously existing library at the new location" (under "Switch/Create library") means.
On yet another only tangentially related subject, I am using Linux Mint with Calibre and Kindle Laptop Reader but have not been about to get Adobe Digital Editions to work on Linux Mint.
And finally, while I'm at it, anyone know of progress in adapting Hoopla to the Kindle (or Calibre)?
I apologize for throwing all this in one post, Moderators, but remember, it's Christmas!