Greasemonkey Script: Sticky Notes [Update 4]
I wrote my first greasemonkey script: Sticky Notes. With this script you can add sticky notes to every website. However, because this is my first greasmonkey script don't expect it to be perfect.
Update:
Now you can resize the sticky notes, there is no longer made a distinction between URL and URL#FOO, and I have also proper z-ordering implemented.
If anyone could tell me why moving and resizing the notes is so buggy I would be happy.
Update 2:
Moving and resizing is now much more stable! :)
Update 3:
With a little help from Mihai I added support for custom stylesheets. Now you can theme your sticky notes as you wish.
Update 4:
Tiny improvement: moving/resizing sticky notes should now work on more websites (because now I install some event handlers at the right place).
Also it's now possible to add sticky notes through a bookmarklet. Just add this link to your bookmarks.[1]
Download:
Sticky Notes on userscript.org
Screenshots:

PS: You may use this script under the terms of the GPLv2 or GPLv3.
PPS: I added it to userscripts.org.
Notes:
[1] I'm not completely confident with this because I have to use unsafeWindow for this feature.
Update:
Now you can resize the sticky notes, there is no longer made a distinction between URL and URL#FOO, and I have also proper z-ordering implemented.
If anyone could tell me why moving and resizing the notes is so buggy I would be happy.
Update 2:
Moving and resizing is now much more stable! :)
Update 3:
With a little help from Mihai I added support for custom stylesheets. Now you can theme your sticky notes as you wish.
Update 4:
Tiny improvement: moving/resizing sticky notes should now work on more websites (because now I install some event handlers at the right place).
Also it's now possible to add sticky notes through a bookmarklet. Just add this link to your bookmarks.[1]
Download:
Sticky Notes on userscript.org
Screenshots:
PS: You may use this script under the terms of the GPLv2 or GPLv3.
PPS: I added it to userscripts.org.
Notes:
[1] I'm not completely confident with this because I have to use unsafeWindow for this feature.
panzi - 11. Mai, 04:13

If you change the file extension to .user.js the Greasemonkey installation dialog will automatically appear.
save to file
As far as I know this is not supported by greasemonkey. However, this scrip already provides a export/import functionality where you get the text you have to save into a file in a textbox. You have to copy+paste it to/from a text file yourself (be sure to not add additional blank lines).