Gnome programs should allow saving/opening encrypted files using one unified
encryption format.

This is how I imagine this could work - using gedit text editor:

1) User edits a document in gedit,
2) User saves the document using "Save As"
3) User selects the location, name for the document, selects the checkbox
"encrypt file" and saves the document
4) User is prompted to enter a password twice
5) the document is saved as "document.txt.crypt" or something like that

Using one unified, system-wide encryption format (which could be in some
library) would ease writing programs which support file-encryption (because the
authors wouldn't have to invent their own stuff, but use what comes with Gnome
instead).

If the application wouldn't (yet) support Open/Save encrypted files, a helper
application (named KCrypr or similar) would allow him/her to convert the message
from .txt format (or .jpg, .eml, .whatever) to .txt.crypt (or .jpg.crypt,
.eml.crypt, .whatever.crypt etc.), and convert them back to not-encrypted format
(enter password etc.).

This would come handy in the following cases:

1) storing documents on floppies/CDs/USB-sticks (which you can be lost)
2) storing some important documents on laptops (which can be stolen)
3) sending encrypted files in an enencrypted messages (not everyone can enable
email encryption; and then read the encrypted message; KCrypt program would come
handy)
4) storing important documents on a PC (not everyone can use encrypted
filesystem etc.)
5) no OS / desktop environment has it yet (I think) :)