I didn't know Calibre had an app; I thought it was strictly software.
Do any of you use to manage your main library? I've always just used Windows Explorer. I get my ebooks from a lot of different sources and I can see where Cablibre's tagging and organization could be useful.

And... my big beef with public library checkouts has mostly been solved. Public libraries set the checkout period with Overdrive. Our system "expires" books after two weeks. They still don't have a renew option, but you can go and get the same book again after three days.

I've had mixed experiences with the DRM stripper used with Calibre. Format conversion is super easy. I've even fixed some f-ed up PDFs to epub conversions (format issue) with the tools in the software.