Efficient? Maybe, but this basically means that my book collection is tied up with Calibre for the rest of my life.
Not really - just treat it's directory tree as a DB and recall you can easily export it to whatever structure/format you want, whenever you want.
They should pull a Trent Reznor and re-submit the app.
He did, but it looks like the same reviewer bounced it for the same reason, without taking on board any of his comments about it not itself having any content itself... He did later get a request to remove "this particular section" of his app, which suggests the reviewer still didn't understand what the app did (i.e. provide a search/download/read interface to PG).
You do not have mail.