I was thinking of kded too. And then making a plasmoid for it would be an extra.

2008/5/1 Bernhard <mustermaxi@gmail.com>:
hm.. personally I don't think that a plasmoid is the right way for this... an average user isn't interested in the number of process ids left and shouldn't have to add a plasmoid for checking for free space.
I'm not familiar with the internals of KDE but maybe kded is the appropriate place for these checks.

2008/4/30 Allen Winter <winter@kde.org>:
On Wednesday 30 April 2008 14:26:07 alessandro diaferia wrote:
> Hi mailinglist, some minutes ago a guy aka spiroo in #kde-devel suggested
> to make a sort of realtime check of running out of space while kde is in
> use. Maybe this check should inform users that space is running out.
> This suggestion is discussed here
> https://bugzilla.novell.com/show_bug.cgi?id=199054
>

I offer up an idea I had a long time ago, but probably never talked about...

A plasmoid that does some basis system monitoring like:
 running out of diskspace
 running out of processes
 someone remotedly logged into the machine
 etc.

sorta like the "check oil", "low on fuel".. lights on your car dashboard.