I've read most of the bookshelf books on my quester. The only ones I don't read are

1. Duplicate books (there are a lot of duplicate books in bookshelves)
2. Bookshelves in Delves and such next to enemy spawns (why ZOS) can't read em properly as mobs respawn and aggro
3. 'The Last Year of the First Era' series books. Idk it's just boring to me

when i'm actively questing i read absolutely everything.
ooh and aah at every crate and wall.
maybe take off my weapons, punch this quest "bOsS" to death.
immersion, baby!

The only reasons I don't read books are:
1) I've read it before and still remember it
2) I'm in a group and don't want to hold them up

Sometimes it's not very interesting to me, but since most of the books in ESO are incredibly short (a lot are just the initial 2 pages, and that's with large text) that's usually not a problem.

I also picked out 200 books to have in my main characters' house, and 4 of those to have around the place as ones they're currently reading.

Rarely. ESO has trained me that reading a lorebook invites a respawn of baddies on my head. Seriously, I've been attacked way too many times trying to read something to be bothered.

Always when I'm alone, if I intended to click on the bookshelf. Once in a blue moon, when I'm in a rush and don't have time to stop at every bookshelf, I'll accidentally click on one while trying to do something else, and then I usually close it right away, especially if I can tell it's one I've read before. But generally speaking, I try to read through as much as possible.

If I'm in dungeons, especially when using the group finder, I don't click on anything, unless there's a lorebook I need to pick up, in which case I don't read it unless I'm already waiting for someone else. That being said, I try to speedrun back through the dungeons to pick up anything I've missed after the final boss, either after everyone else is gone or if someone else has asked me to wait while they finish the quest, look for chests, etc. (If someone else asks me to hang around a few minutes, I will always do it, basically 100% of the time.) So if I'm not holding anyone else up at that point, I will read through the books.

I read them if it is associated with a quest and there is a puzzle whose solution is hidden within the text. Anything else is just looked at to clear the lore book entries as I can go back later and read should I wish to do so.

If I wanted to read, I wouldn't be playing a game.

Almost always, i.e. when I play solo, which is most of the time at the moment. It doesn't matter how many times I have read them.

It helps that one of my characters purposely seeks out lost or discarded books on his travels and, once found, can't help but open the cover...

It's funny, because I'm super narrative-focused in how I play, but I don't tend to read them too much. I think it's because of how the books exist in the world--in the singleplayer games, if I see a book I want to read, I'll grab it off the shelf and pick it up later, at a more convenient time. In ESO, my options are either to A) read it right away at the bookshelf or B) remember to search for the book in Eidetic Memory at a more convenient time.

The system is fine, but when my character is going about her day, it doesn't really make sense for her to just drop whatever she's doing and read a whole book. Even if that book would fit in a single page in MS Word, heheh.

I always read the quest-related docs straight away. I pick up the lore books as I go along and then read them from eidetic memory later on.

I don't even read the story dialogue half of the time in quests anymore. XD

Only read them on my first play-through. After that, click-it and forget-it.

In Skyrim I collected books in my house and occasionally logged on just to read them. Here, I follow a similar pattern and log in just to read my collected lore from time to time but rarely stop to read them "in the field" unless they pertain to the quest I'm on at the time.