Server Overload

I've seen brief posts regarding server loads, distrubution for heavy loads,
etc, but don't recall if there were any solutions...

Anyways...We are running a Postgres DB against multiple frontend
webservers.  For most of the time, everything runs fine.  Then, all of a
sudden, everything will start to go all funky.  Crashing...Errors...Etc...

When I log onto the DB server and try to do anything, I get "Too many open
files in system."  ulimit is set to unlimited and there is PLENTY of FREE
memory.
I shut down one of the frontend servers to clear some connections to the DB
and then start it back up and everything seems to be back to normal.

Has anyone experienced anything similar?  Does anyone have any suggestions
on what I could try to do to rectify this problem?

Any comments and/or suggestions are much appreciated!

Thanks.

Arthur