If you were going to do this, it would be cool if this metadata was
associated with the document itself. That way when you update the file
or copy and paste text somewhere into it, your bookmark to line 86
will correctly redirect to line 215 where the bookmarked text now resides.

Do the original reporter really mean *lines*... what's the point of bookmarking
a line??

Its quite useful to mark several points in a file so that you can
very quickly move between them.  Especially handy for large
source files.

Also many editors have a "mark lines matching this pattern" option
from the find dialog.

And of course this should be implemented as a plugin to keep the default UI simple.

We are moving all the request for plugins that we don't plan to add to gedit
itself on http://live.gnome.org/Gedit.

Closing as WONTFIX.