Which of the features of the GUI are most convenient for thesaurus managers?

Relations between concepts can be added via simple drag and drop of concepts. Auto-complete helps to re-use existing concepts when adding new terms.

Merging of two concepts can easily be managed via drag and drop (drop the concept you want to merge on the altLabel section of the target concept and all relations and labels will be merged to one concept).

Provision of several (also customizable) skins (incl. a Windows Theme).