Ten years ago,
Bill Gates bemoaned competition undermining Microsoft
"Our DOS gold mine is shrinking and our costs are soaring--primarily due to low prices, IBM share, and DR-DOS."
This evidence came out in Caldera's lawsuit against Microsoft
for predatory practices against DR-DOS. Bill Gates goes on to
say "I believe people underestimate the impact DR-DOS has had on us in terms of pricing"
Update: 03/31 11:36
More info at Caldera's website
is quite interesting,
for instance detailing Vobis' attempts at using DR-DOS instead.