If I may insert myself in this thread,
I wondered about the same things for some time...
Given the time I spent inserting & manually editing the records for my books, I'd like the result to stay alive&working as long as possible.
Of course I wish Kovid a long and productive life, but what happens if he for some reason stops developing calibre (or is kidnapped by aliens, or ...)?
That's the reason we like open formats - as Calibre is, luckily.
Therefore I am very interested in any info regarding <alternative> ways to delve into its structure. And since this structure is documented, any problems will surely be due to the operator mishandling it - backups are there for a reason...
So, any info for hacking the database is welcome (I saw some people in other threads mention SQL queries, time ago), and if the thread can be made sticky, all the better
alessandro