Monitor power management

[Mark Styles <gnome lambic co uk>]

I have an odd problem and I don't know where to start tracking it
down. When I first log into a Gnome session, my monitor will go into
power save mode after a few minutes of inactivity, but after a day or
so of being logged in, it stops doing that and the monitor stays on
all the time.

Any thoughts on why this is happening, or where I can look to
investigate?

Thanks
Mark Styles