Most of the large ISPs in the US run IS-IS as their IP IGP.
In europe a number of PTTs have chosen IS-IS as the IGP for their new
IP Internet backbones. That might be an indication if IS-IS is dead.
This points out the real issue. OSPF and IS-IS are close enough that other
factors usually outweigh their differences. The choice of IS-IS in this
case is really the result of the choice of an equipment vendor. These days
at least, vendors are not chosen because they implement IS-IS. IS-IS is
chosen because of some vendors' protocol implementations.