I noticed a few times that I would be working on my computer, leave for a while and when I come back every thign is slow and jerky. Firefox stops scrolling, Videos are suddenly jerky. Programs took forever to open and trying to edit a video was pointless.
The give away was that the hard drive light was continually on. As a test I left it running to see how long it took to stop. It was still thrashing the hard drive 11 hours later !!!!
It took ages to find the problem, but eventually I noticed that whenever this was happening a program called gvfs-metadata was running.
Eventually I took a chance and went into synaptic and deleted everythign with gvfs in its name.
My system is great now, but... Every now and again I notice the problem again. It seems some Gnome applications install it. The last one was Nautilus. Now if I notice this happening I simply go back into Synaptic and delete anything with gvfs in the name.
Such a simple solution to such an annoying problem.