I am running Suse 10.0, I haven't changed any hardware or software, it has been running fine for two years. It happened overnight. Right now the mouse moves as if the CPU is 100% and out of memory, but the system is just running fine, the keyboard is responsive and all the programs run just as fast as before. It is just the mouse, it moves very sluggish and slow. I checked the log and xorg.conf, nothing suspicious turned out. The mouse works well on my XP box.

Anyone has any idea where to start to trace down this?

Control center - Peripherals - Mouse would be a good place to start.

Actually I tried, I reset it to default, but it didn't change anything. Also the xorg.conf is like 6 month old and never been touched, so it is also not the cause.

I can only really say that I've seen this too (not SuSE, that worked fine, but Debian and Fedora installs on problematic hardware).

What I saw didn't seem to be the mouse, per se, but the OS not reacting fast enough to 'mickeys'. I suspected:
- poor choice of scheduler
- something with the bios causing, eg, the ACPI set up to be 'bad' resulting in the use of 'pseudo-interrupts'
- bad swappiness value
- or, maybe, something bad going on in the background (and sometimes that can be difficult to spot)
but I decided against chasing it down and I don't see why any of the above would have changed overnight for you.

It is some sort of communication failure in the USB driver at kernel level. I never saw this problem before 2.6.19, so it must have been something that was added. I also seem to get the issue more when i have a lot of high disk activity.

It requires a reboot to sort the mouse out. Never seen the problem in windows though.