I think the post by CWatkinsNash in combination with the others above is an example of one of the reasons why the other attempts to change the UI have failed. Trying to get users to define what they use Calibre for and then extrapolating meaningfully from that is an almost impossible task.
For a start your "sample" is going to be heavily biased by those who contribute to these forums, which by their very nature will be biased more towards the power users of calibre who are more comfortable with technology in general (but represent a teeny fraction of the calibre users). The example by CWatkinsNash for instance lists a whole bunch of stuff that I too do on a regular basis as will many others in these forums - but I would also bet the house that the vast majority of calibre users do not do half those things.
I also believe that the vast majority of users use only a fraction of calibre - but quite possibly different fractions as they have different use cases. Some people here are totally into "News", some are massively into conversions. Some are plugin addicts, but the vast majority of calibre users wouldn't have a clue what a plugin is. Some use the web hosting, some the cataloging. Some are metadata perfectionists, many others have never tried it.
Now before you think I am trying to shoot your intent completely down, as I have posted in the past I 100% agree with you that the calibre UI has potential room for improvement. I went through exactly the same process as you in setting up calibre for my parents, installed it, configured it, customised the toolbars and menus to simplify down to minimal for what they might need, and its still very intimidating without patient hand-holding. The same for even technical friends of mine - I have to explain a whole bunch of settings to change away from the defaults etc, because they want something out of the box that just does what they want without spending hours of tinkering and trawling the forums. Some of us are willing to look under the hood and find out what many of those options mean/do, but I would suggest many others just want something to manage their books onto their device with no faffing to spend more time reading.
My parents use case which might be relevant to your own is fairly simple:
- they can browse books using the tag browser (they would never type a search!),
- they import using the second option in the Add dropdown from a Dropbox folder I put them into for them (wish I could make that the default for the Add button),
- they never do conversions or download metadata (since I do it for them)
- they track whether they have read a book in a custom column
- they send books to their Kindle using Send to Device and the Kindle Collections plugin, and remove from their device when read.
- Dad recently decided he wanted to have separate libraries for his and Mum's books, so now he uses the Copy to Library function and switches libraries.
My own usage is far more complex and hence not relevant to this thread I think. That said, even doing things like Conversions there is only ever about four settings I will tinker with depending on the book - setting justification to full, smarten punctuation, heuristic processing on the very rare case of attempting a PDF conversion, and equally rarely doing a split of pages based on a heading style after tinkering in Sigil (just to reduce # of manual splits). All other editing/settings I do in Sigil on the ePub directly.
Some might argue there is almost a case for two different UI's for calibre. However that is a non-starter, as Kovid and the other devs will not want to maintain two UIs. There are some functions of calibre fall into the "advanced" category that you might want to "hide" from beginners - but as an advanced user you will be spitting tacks if stuff you use all the time is now relegated into some obscure popup that takes extra clicks (which is why some UI suggestions here have failed in the past).
One suggestion I made a long time ago is I think more work could be done on the wizard for first-time users. People who want author names as LN, FN should not have to come to the forums and lean what a "tweak" is. Equally people who have a Kindle (which lets face it will be a significant portion of the user base) should not have to come to the forums and learn about metadata plugboards. There are a number of other examples of settings which could be offered just as dropdown defaults on the wizard. If over time the user wants to customise them further they can - but many users in the "beginner" category will not want to have to learn that stuff just to get started, if ever.
Good luck... like many we will be intrigued to see what suggestions you can come up with.