The current Gnome Session Preferences suffers from an number of problems which impacts its usability.
When there is only one session, the default, it does not show up in the sessions list. The tab provides no method of editing the current session. This has to be done in situ (ie the user logged in to the particular session they want to edit), with the user saving session upon log out.
This tab displays the dynamic state of the current session, it does not show what the static attributes of the current session are. Personaly I think the Order and Style attributes are confusing. Note: I am also running GIMP here and it is not showing up, because I guess it doesn't support GNOME 2.x SM.
And here we have something that deals with programs that do not support GNOME 2.x SM. Its not clear that this feature applies accross all sessions not just the current one.
And of corse Solaris's dtlogin doesn't support gnome sessions, so any session a user might create in Solaris, won't be visible in their login screen.
Assumption: Session is a nasty term and should not be exposed by default to a user
Assumption: Quick fix for Solaris
The idea here is not to expose the nasty implemenation model, and have one bucket for all startup apps. The notion of mutiple sessions would be removed from the GUI until gnome sessions was properly fixed.
Keep the current GUI the same for linuxes that use GDM.
For Solaris (and Linuxes that don't use GDM)
The rest could mostly stay the same with some tweaks.