Roll Your Own Name Service

[Startup Consulting Company]

I'm curious about approaches that are used
to create name services under UNIX.  Are Sun's
White/Yellow pages the only widely used standard?
If you were trying to get a list of all the users on
all UNIX machines in a well-defined Internet, how would you
do it if some users were using white/yellow pages, others
were using OSF's directory service, etc.?  

Dave