I was surprised as you are, and would probably be if you'd heard that
since 2000, numerous people have tried to snowboard down Mt. Everest.
"There have been 15 ski descents from Everest before, but only one
complete - from summit to BC: On October 7, 2000 Davo Karnicar skied
down from the summit on Everest south side. Hans Kammerlander skied
down the north side in May 1996, but his descent was from 7800m and
not complete. "
(SOURCE: Mt. Everest, "Everest Viking skier update: Search for Tomas
Olsson difficult, veterans say",
Of them, "Marco Siffredi snowboarded down the Norton Couloir in 2001,
after summitting through the normal route with Himex. Only one year
later, on September 8, 2002 Marco attempted a snowboard descent of the
steep Hornbein Couloir. He arrived at the summit at approximately 2:00
p.m. and waited for about an hour for the clouds to dissipate before
starting on his way down. Teammate Olivier Besson watched Siffredi
through a telescope at Advanced Base Camp. At about 3:30 p.m.,
Siffredi slipped from view and was never seen nor heard from again. "
(ibid). He was only 23. :-(
Sarah Smith, "Everest Snowboarder Vanishes On Second Try", National
Stephen Koch, another famed snowboarder, has also wanted to snowboard
the mountain, but gave up - according to Koch, this mission would be
Facing the Fall Line
I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it. My search term:
[snowboarded down Mount Everest] etc.