I don't normally read more than one book at once, but if you'll check the sidebar, you'll see that is indeed what I am doing right now.
I started Indian Givers first, but while the book is very interesting, it's also easy to get burned out on. I had checked out and downloaded Willow to my Nook as a test (to see if I could put library ebooks on my micro SD card), so I decided to read that at the same time as Indian Givers.
And of course there is the read in-store feature — I've even given that its own section in the sidebar. With the Nook you can read some ebooks for free an hour every day when you are in the store, so I decided to try that feature out on one of the books on my wish list. Not all ebooks are available for read in-store, but I found one that I wanted to read (but didn't necessarily want to spend the money on). Since I can only read it for an hour a day, and we only go to Barnes & Noble once or twice a week, it'll take a while to finish, which is why I made "Reading In-Store" its own heading.
Like I said, I don't usually read more than one book at once, but I've found it's nice to read a short novel at the same time when you're reading nonfiction. And of course, I will probably always be reading at least two books at once now, so that I can take advantage of the read in-store feature.
What about you? Do you often read more than one book at once, and why? How many at once is the norm for you?