The option exists to transfer segment ownership from user to user in SiteCatalyst 15, but not in Discover/Ad-Hoc.
Some of those (shared) segments are used in report builder, sitecatalyst and data warehouse, and they are linked to those various reports or data feeds via their internal ID number. Without the ability to transfer ownership the segments not only need to be recreated, but also re-selected and applied to all reports/views/feeds that depend on them.
Please add this basic functionality and make segments more manageable.