As a reader, I do take note of typography. While it doesn't necessarily make or break a book, it does directly impact the ease of which I can read a book. If you've never really paid attention, take a second to do so and then think back on those books that something just seemed not right.
Traditional design denotes that use of a serif font is the easiest on the eyes for reading -- those serifs help in defining a line moving the eye from letter to letter. You can't see the line, but it's there. Sans serif fonts, however, are smoother but do not help in defining a visual line for readers. They look more contemporary and are great for emphasis or for titles since they just stand out. I've read, too, that the sans serif is easier on the eyes digitally; I'm not sure simply because I haven't spent enough time reading longer text blocks on a screen to notice a difference.
Most books are printed with serif fonts, but I've noticed a trend lately in that more books are published with the sans serif font (perhaps something to do with the fact we're more accustomed to digital text which trends sans serif). It's been a tripping point in my reading, too: I find the books printed in sans serif harder to get through because they require more effort on my part to read, and they suffer from the challenge of being less able to define emphasis or tone through font shifts. An advantage of the serif font is the versatility in developing tone, character, or emphasis through use of the sans serif.
Here's an example. Justine Chen Headley's recent book North of Beautiful is set entirely in sans serif font. You can preview the first couple of pages here. Now, compare how you read that with how you can read the first few pages of Shooting the Moon by Frances O'Roark Dowell here. While the first one is definitely more aesthetically pleasing, I find the second much easier to read. My eyes can more easily glide across the lines, whereas in the first one, I have to spend more time on the process of moving my eyes. Sure, it's fractions of a second, but over the course of 300 pages, it makes a difference.
All of this is to say that I find this trend an interesting one and one that perhaps isn't entirely helpful to readers. What do you think? Do you have a preference for typography? I think it is definitely worth noting this and considering it as we read. It's not about the font choices, but it's important to think about typography and on how the reading experience was enhanced or hindered because of that choice.
You can read a bit more about typography as a design principle here. I'd love to hear your thoughts or experiences regarding the serif versus sans serif issue. I think there are beautiful fonts in both families and both have a place in a book; however, the use of the sans serif, I think, should be off-limits for the bulk of the body of text.