There's nothing painfully wrong with your current design, especially if you're a developer with little existing knowledge. I would add more whitespace into your front page. The elements feel as though they are sitting on top of each other. Adding some breathing room will also help your visitors scan the page more easily.

I'm not much of a designer and have stronger programming sense. But I know what looks good. So sometimes, I'll go through my bookmarks, RSS feeds of idea sites, or check out website templates to get ideas. I might even take one and tweak it to my own tastes.

Also, see if you can go to a hackathon nearby and find an awesome designer to work with. Make sur eyou sit next to him and casually watch how he works. I did this last weekend it was an awesome way to observe a designer working within in his element.

From a usability point of you, your approach is direct and intuitive. Everything does what it seems like it should do. I wasn't surprised by anything. The interface is really snappy. Took a look through your javascript and you have excellent, well organized, well documented code. Beautiful!

Regarding improving your user experience... take a cue from Google and see if you can implement a realtime search as the user types. People are suckers for instant gratification. Maybe you can tie into a book preview service and offer an inside look of the books from the search page? I don't know, just a few off the wall ideas.

Great job with this otherwise! Hope this helped.

Cool project. My $.02. :)