It's really easy to use. You can delete books when you're finished. If they're ones you got from Amazon, they keep a copy in your online library, so if you ever want to read it again you can download it again for free. Or you can copy it to your computer before you delete it. It takes less than a minute to get a book delivered to it from Amazon. This is really tempting when books you're dying to read come out-they'll be electronically delivered at midnight. When Charlaine Harris's last southern vampire book came out I had to force myself to go to sleep instead of staying up waiting for it.
There are lots of ways to get free ebooks online, and you can find free programs for converting various formats to formats supported by the Kindle. The new, bigger Kindle can read PDFs without conversion; the one I have they have to be converted to something else. I use Mobipocket to convert them; it's a free program. You really don't have to be very tech-savvy to use it.