Yeah!
Here you go. This patch allows to password-protect any item I have come across so far (though I could only try with books, PDFs, Kindlets, and notifications). It should work for pretty much everything that has a details page (long-click the item), but I cannot be 100% sure.
If you experience any trouble, please let me know. And if you don't, feedback is still appreciated!
Localizations for english, german, french, and italian, are included. Additional localizations are more than welcome, as are corrections to the currently included texts. Simply take a look at (and/or modify) the ixtab-patch-passwd.txt inside the zip, and reply to this thread if you have suggestions.
INSTALLATION:
Copy the attached file directly to the opt/jbpatch/ directory on your Kindle (do NOT unzip the file!). Add the appropriate entry ("ixtab_passwd-5.1.0.zip") to the CONFIG.TXT in that directory, then restart your Kindle.
Technical notes:- Passwords are stored in /var/local/ixtab-patch-passwd.bin. If you remove this file, everything is "unprotected" again. The same is of course true if you disable this patch (duh!).
- Collections are not, and will not be, supported.
- Passwords are tied to the UUID of an item. The UUID is stable as long as an item exists on the Kindle. If you remove, then re-add, or if you replace an item, the UUID is likely to change (meaning that password-protection will be "lost" and has to be set up again).
- Source code is here.
UPDATE 2012-05-21
Included italian localization, slightly improved the french one.