"By "use" do you know if they mean in a positive or negative manner?"
Good question!
I suspect there is an element of 'conflict'.
There will be people who would like bikes banned, but under Access legislation people have a right to cycle in such places. BUT the right comes with responsibilities.
People (particularly young ones) have always cycled on Corstorphine Hill, now it's legal - if done responsibly. That may mean not cycling at speed across paths walkers use, or causing erosion, or riding in sensitive wildlife areas.
"The ranger service in the pentlands tries to direct mountain bikers to specific paths in their printed materials"
I think that has generally worked. Paths have to be 'closed' sometimes - usually because of erosion after wet weather...
There can also be issues with livestock where it's often irresponsible dog owners who cause problems.
Incidentally -
"
In April 2012, the Countryside Ranger Service merged with the Pentland Hills Ranger Service. Based at the Hermitage of Braid, they are now called the Natural Heritage Service.
"
http://www.edinburgh.gov.uk/info/78/countryside_management_and_conservation/710/natural_heritage_sites/1