Is it worth paying an extra tender for the “without ads” option?
Now that the Kindle can display the book cover when it's in standby mode, I think it's worth the extra tenner. One of my bugbears was that you used to forget the name of the book you're reading and who wrote it. For me, that simple change has improved the experience a lot.
Another great website for Kindle users is http://ereaderiq.co.uk - you can track any Kindle book's price and be alerted when it's cheap. There are a lot of short term deals, even on new titles. Free to use, other than voluntary donations.
On the downside, I already have more books stored up than I will probably be able to read in the rest of my life. It gets a bit addictive. But they haven't cost much and don't take up any space in the house... if they did, I'd be addicted AND divorced