It is only after many excellent (but sadly many lost) analysis by Sokolsky and many of his correspondence trials (and even OTB games!) that this opening really got serious treatment. Sokolsky (and later Katalimov) produced the first serious study of this fantastic debut and even played it!
Nowadays, top players at the international level
(OTB) almost never play it (except for Ljubojevic and Larsen
in their early days) and the Orang Utan is usually used for its element
of surprise. The only known exception that I know is Gilles Mirallès
(France champion) who played it for most of its career. Besides these
few trials in OTB games, the Orang Utan opening is mostly used in correspondence