Kindle 3rd Generation
In the Kindle 3rd generation (latest) you can add a bookmark at any place, and you can also have several of them if you want. It does automatically bookmark the page you are reading.
Place a Bookmark
To place a bookmark in the book you are reading, navigate to the page you want to bookmark and press the Menu button. Underline Add a Bookmark using the 5-way controller, and then press the 5-way controller to select it. The bookmark will automatically be added in the upper right-hand corner of the page.
If you want to remove a bookmark you have already set, navigate to the page in the book that is bookmarked and press the Menu button. Underline Delete Bookmark, and press the 5-way controller. The bookmark will be removed automatically. You can also hold down Alt + B to delete a bookmark.
Remove Several Bookmarks At One Time
If you need to delete several bookmarks at one time, press the Menu button, underline My Notes and Marks, and use the 5-way controller to select it. Navigate to the bookmark you want to delete and press the Delete key. Repeat these steps to remove the other bookmarks.
To view the bookmarks you have already set, press the Menu button, and then click View Notes & Marks. You will see a list of the bookmarks you have set in the order that they occur in the book. Each bookmark shows a location number, and the first line of the location. If you want to go to that bookmark, navigate to the bookmark and select it with the 5-way controller.