I'm with weedfreak in wanting the option of no icons at all. If I needed to point at pictures instead of read text, I wouldn't have much use for ebooks.
On a related note, it's generally considered a better practice to gray out invalid icons, just like menu items, rather than making them disappear and reappear. That behavior is a tad disconcerting.
And while I'm being all quibbly, perhaps the icon width allowance could be made aware of the regular/widescreen settings? Spreading the little suckers out a bit so that the text fits at small icon sizes would be nice, especially for the library/device ones. There are two reasons that someone might want small icons -- one, if they have a small screen (say, my netbook, if I ever dared try to run calibre on it), and two, if they just hate pointing at pictures. Maybe some sort of preferences setting to indicate which it is?
Anyway, aside from that, I love 7.10 so far. *loud fannish squeals of glee*