My quick 2 cents:
The goal of a parallel startup is to plunge the user into the graphical login as quickly as possible while the remaining daemons continue starting in the background. This gives the feel of a faster startup and in reality does just that with limited functionality as remaining services come to life.
To this end i would create a tree style dependency graph (gantt like) of services as they are installed on the system. Services can specify that they "require" a particular service to be started or simply "request" that a previous daemon be started before it is started (in the first case the current service wouldnt be executed if the dependent failed in the second it would with supposed partial functionality). Every daemon on the tree should be started eventually but particular ones could be fast forwarded by adding them to a specialized queue. The queue is sorted FIFO style and its dependents are added to an independent FILO stack that starts only those services required to get you to the point at which the queued service can run (utilizing parallel startups where possible of course).
In the event a service fails the user should be notified and any service that "requires" it shouldnt be started but any service that "requests" it should be with partial functionality. Am i making any sense to other people or am i way off base? This allows you to get into a "working" environment as quickly as possible while also starting the remaining services as efficiently as possible. Feedback always welcome.
--mf
