Not a complaint. Just a suggestion with a solution in my opinion. You don't have to accept it obviously.
Perhaps you misunderstand me. I don't mind frequent updates. I actually like to, as chaley says, 'get stuff hot off the press'.
But I was talking from a point of view of non tech users. Calibre is a very popular software and the targeted users are not technically proficient in general. They are not concerned with the fact that calibre is mostly in beta stage. They get a software that is highly recommended everywhere and expect it to work flawlessly.
It is also a fact that even the general users like to update as soon as an update is available, specially when the software itself tells them so, regardless of whether they need the fixes/features in the update or not.
My suggestion is to add two options to update notifications. One as it is right now and the other after a small time period. Say 3 days or 7 days. There is no need of a rigorous testing phase or beta testers. It would be obvious if any big flaws creep in an update from the immediate updater users.
I think this would greatly improve the perceived stability for such 'general users'.