Originally Posted by sirmaru
Just open Options and tap "Notes." Tap the pencil icon on the top left. Then close "Notes." Then tap the Bookmark in the upper right hand corner and you will be given a virtual keyboard and an option to write a Note for the Bookmark.
If your tap in the upper right corner doesn't create the bookmark, you can just tap the bookmark icon with "Notes" open from the Options Menu. I find that a lot easier then tapping the upper right hand corner.
You can also type the note in the Reader Libary and sync with the PRS 900.