This manual page documents briefly gksu and gksudo
gksu is a frontend to su and gksudo is a frontend to sudo.
Their primary purpose is to run graphical commands that need
root without the need to run an X terminal emulator and
using su directly.
Unfortunately the man page doesn't currently (I'm logging a bug) say anything about the changes made for integration with OpenSolaris RBAC (LSARC/2006/348).
If the user has an RBAC profile entry to run the command, given as the argument to gksu, then gksu will execute the command using pfexec(1).
If the user doesn't have a direct RBAC profile entry for the command but the user can assume a role that does have an RBAC profile entry then gksu prompts for the role password and uses the role. In this case gksu is doing the exec using embedded_su(1M) (which is really a hardlink to /bin/su).
Failing all that then gksu prompts for the root password; which will fail it root is a role that the user can't assume.
Menu entries for things like packagemanager, updatemanager, printmanager on OpenSolaris already do use gksu(1)
gksu by default does a full X keyboard and mouse grab while prompting for the password. It also passes on the users X magic cookie so GUI programs work well.
gksu can also use sudo as the back end instead of OpenSolaris RBAC or embeded_su, that is standard gksu behaviour though not something specific to OpenSolaris.