Good typography is pretty important to book cover design. Actually, I believe good typography is important to most things, but I know that isn't a universal sentiment.
At Rock That Font , the importance of good typography on album art is focused on. Specifically, the site "celebrates the union of rock’n'roll and typography, both old and new".
Here's a video of site founder Shawn O'Keefe talking about how Rock That Font started:
In the video, he discusses the new album by The Black Keys, "Brothers" and the use of Cooper Black on the album cover. Before I watched this video and read the RTF entry on "Brothers", I had no idea drummer Patrick Carney's brother Michael had designed all of their album covers (Apparently I am slacking in my Black Keys fandom). O'Keefe says the use of Cooper Black is so successful here because of its "raw, youthful blues-rock vibe, but in a unique way. I think the cover is just an awesome representation of the Black Keys and their music.
In their most recent entry is on Arcade Fire's "The Suburbs", one of my favorite albums from 2010 and maybe of all time. I really love this cover for it's colors and imagery that fits with the tone of the album, and the type accompanying it is pretty perfect, too.
Also in the video, O'Keefe says something I think non-typography nerds would laugh at but I believe hits home: "When typography is working we don't even notice. We feel it; its in our gut. When it doesn't work, we do notice."
I've already bookmarked Rock That Font and plan to visit it regularly. Awesome work.