[fjtorres]

For me, using a cover is mostly about ergonomics:
The oh-so-popular thin slab form factor with the typical narrow frame doesn't me offer a comfortable grip. Great to look at and carry but come reading time, not so much.

So, since I typically read dual column landscape, the cover spine helps me balance the weight and gives me a couple different ways to hold it.

Of course, ye olde PB360 and RB-1000 don't have those issues or need covers for that.
With spinal designs due for a comeback things may change. I'm looking forward to the next wave of China, Inc readers and Eink tablets.