Actually in Select menu there is two items "To Path" and "Save To Channel".
I searched long time how to convert selection to brush, I think that the only way was to save brush to a file, move the file to ~/.gimp-xx/brush folder and restart gimp.
This week in a newsgroup, another guy searched didn't find how to convert a selection to a pattern. For him the only way was to save selection to move the file to ~/gimp-xx/pattern folder and restart gimp :(.
A day, don't know exactly for why, By wandering in gimp menus, I find the miraculous:
Script-Fu->Selection->To Brush/Image/Pattern
I believe (perhaps wrong), that the human logic is to use the same tool to do nearly the same thing.
The menu Select could have an organisation for these conversions as:
Select->To...->[Brush/Channel/Image/Path/Pattern/...]
to avoid a to long Select menu.
and a 'Selection To Brush/Pattern' button could be in brush/Pattern windows, as there is 'Selection to Path' button in Path window.
This could improve speed of The Gimp apprenticeship and workflow for some tasks.
Regards
Popolon