The issue with using one trash is that deleting something from a removable media would require to copy it to the local disk which can take some time. Not having a trash on removable medias is bug #12893 and will be fixed
-- Trash always empty. https://launchpad.net/bugs/34247 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
