I got an e-reader as a gift. I like it for travelling since I can just grab it and go and not worry about what kind of book reading mood I'll be in once I get there. I only get free books or extremely cheap ones on it, since if I'm going to pay more than $5, I might as well just get the actual book. At least then if I don't like it, I can take it to the used bookstore or give it to a friend. I would say maybe half my reading is done on the e-reader. It's wireless, which is nice, but it has an onscreen keyboard with no touch screen, so that makes entering even simple things kind of tedious.
Basically, I guess I like e-readers, but mine certainly isn't going to completely replace my book collection.