Well, I have noted that whilst the OS boots, the mouse is powered because turning it upside down you can see it glow. But it goes dead just as it's logging in to KDE... So I don't think it's a kernel issue. But then again I note that a package called "laptop-mode-tools" was included in the last update. I'm wondering if this package is causing the issue. The description of this package in Synaptic is:
"Userland scripts to control "laptop mode" Laptop mode is a Linux kernel feature that allows your laptop to save considerable power, by allowing the hard drive to spin down for longer periods of time. This package contains the userland scripts that are needed to enable laptop "mode."
I'm not experienced or technical enough to really know, it's purely a guess.