So many reasons!
1) I live in a podunk little town where the salvation army sells paperbacks for $1.50 and the used book store sells them for $4.50. The library is mostly christian fiction and horror, neither of which I have the remotest interest in.
2) I take public transit which runs every 40 minutes, so I spend a lot of time waiting for a bus. I often read while waiting for the bus, and knit while on the bus. It's a lot easier to shove the kindle in my purse as the bus is arriving than to try not to lose a knitting needle and tangle the ball of yarn in a hurry.
3) My knitting patterns can now be carried around on my kindle - perfect since I was forever losing the page with the part of the pattern I was working on.
4) The bus schedule can be carried on my kindle so I don't have to guess how much longer before the next bus shows up somewhere because I left the DTB version of it in my other purse.
5) So much easier to read! I have occasional back pain issues which make it very uncomfortable to sit or lie in certain positions and the only comfortable ones are impossible to hold a book open in front of my face from!
6) I can use gmail to send a quick txt msg to someone while I'm out and about without breaking out my prepaid cell phone and paying $1 PER TEXT MSG!
7) I have all sorts of files/lists/etc that I can carry with me anywhere now. LOVE that. I shop using coupons and have created my own 'system' that just in 3 weeks has probably saved me atleast half the cost of my kindle in my weekly trips to the store.
8) Oh yeah.. I can read on it too.. pretty nifty that it can do that!
I've been reading more since I got the kindle than I used to before. Which I absolutely love since I hardly read in the last few years - between moving to the middle of nowhere where nobody reads (really, even yardsales don't have books here, it's depressing!) and not having the space to store any fiction once I've filled my shelves with my cookbooks, knitting books, and general craft books (all books that need those pretty glossy images we'll never get on the kindle) I think I must have read less than 10 books a year the last couple of years. I'm currently on book #8 since Jan 29th. I can feel my braincells regenerating each time I sit down to read.