Many Kindle 1 users are selling or giving away their Kindles and upgrading to the Kindle 2. In case you're wondering how to get your content transferred over, here's a quick guide.
Books purchased from Amazon.com
These are automatically backed up in your amazon account, with annotations, bookmarks, etc. Just delete them from your old Kindle. When you're ready to read them on your new Kindle, you can just send them again. From your new Kindle, there will be a menu for 'Archived items'. Select the titles you want and choose download. You can also go into your amazon.com account from your computer, select 'Your Account' from the top of the screen, and then click on 'Manage my Kindle'. You should see all of your purchased books, and you can send them to your new Kindle. You can do this even if you haven't received your new Kindle yet!
Content purchased or downloaded from other sources
Connect your old Kindle to your computer with the usb cable. Copy books or other content from your Kindle to a folder on your computer. You can then either delete the items from your old Kindle, or you can leave them for the next user (if they are transferable). Once you get your new Kindle, connect it to your computer and copy the items onto it.
Amazon Book Samples
If you're like me, you use samples to keep track of books you want to read but are not yet ready to purchase. I had a couple-dozen or so samples on my Kindle 1. Unfortunately, these are not kept in your Amazon account, so you can't just go into your account and send them all to your new Kindle like you can with purchased books. I ended up sitting in front of my computer, with my Kindle 1 in hand, and revisiting each book's product page to send each sample to my new Kindle 2. Kind of painful, but it worked. If anyone has come up with a better way, please leave a comment.