so, not exactly UL backpacking gear, but these things now weigh less than a small paperback. i'm not sure about you, but sometimes i get bored sitting at camp if i'm solo and used to the hustle and bustle of everyday life.
sure, i go into the woods to get away from that, but reading is a great way to pass the time. in addition i can use the reader to store topo maps (as images i import). it's a bit harder to dig out of my pack (than a paper map), and it'd need a plastic bag in rain, but this helps justify the extra weight.
new Barnes & Noble nook: 6.5" x 5.0" x 0.47", 7.48 oz. (212g), 2GB, 6" Diagonal screen, about $140
Kindle3 wifi:7.5 × 4.8 × 0.34" (190 × 123 × 8.51 mm), 8.5 oz (241 g), 4 GB or 3 GB, 6" Diagonal screen, about $100