I have a Kindle and am pretty happy with it. I bought it BECAUSE I have run out of room for all the books I buy. Books are available the same time they are in bookstores and usually cheaper. You can often get a hard back for $8 or so when it's twice that or 4X that in stores.
Downside - it is hard to go back to a specific place if you want to read a part over again for any reason. I have this difficulty when reading history type books and want to compare dates or some such.
Otherwise - the only other issue is that it's too easy to buy a book and not keep track of how much you are spending.