Per-user process limit: ulimit -u unlimited, how to set it for certain users

I'm having no problem setting the max per-user process limit for root,
using...
    ulimit -u unlimited

and I check that it works with
    ulimit -a

But for other certain users that also need unlimited processes, such as the
interchange user, when I run
    ulimit -u unlimited
It doesn't report any errors, but

    ulimit -a
still reports that my per-user limit is 256.

So how do I increase the limit for certain users (besides root)?  Such as
postgres, interchange, etc.  Or what about increasing the limit for ALL
users on a system?

Thanks,

Dan Browning
Network & Database Administrator
Cyclone Computer Systems