After the problems I had after 9.10 upgrade I held off on upgrading to Ubuntu's latest 10.04 (Lucid something-or-other), with kernel 2.6.32-21. Sadly it was another disaster - after upgrade neither my mouse nor keyboard worked beyond the Grub screen.
I looked into it; initially I thought it was an X thing with their new nouveau Nvidia driver but it wasn't that. I then noticed that the devices weren't actually being seen by the system on the USB bus - i.e. when I ran lsusb I only saw a couple of USB hubs (no mouse or keyboard listed) where normally I saw about 6 USB devices - yes they were plugged in and were recognised fine by an older kernel (9.10). I messed about with usbhid kernel module to no avail. I then tried 10.04 live CD and it worked ok with exact same USB setup?! I dumped the output from dmesg and then compared it with dmesg from my machine running the installed version on the exact same kernel version. It seemed that my installed version was failing to recognise the actual PCI USB host controllers on bootup - WTF?! It seems that the ehci-hcd module was not finding the USB hardware.... Smells like a kernel bug.
Finally I tried altering various boot args for the kernel in /boot/grub/menu.lst which didn't work initially, but then I hit upon the right one: pci=noacpi. It now works though my fans seem to be going full speed at all times...
[updated: 21aug10] Unfortunately after the kernel latest update (2.6.32-24) it seems to be totally broken and my fix doesn't work so I've had to revert to using 2.6.32-21 - If you run any DKMS modules (e.g. nvidia) you'll need to have the kernel header files installed that kernel.
Another BIG waste of time....I really am having my doubts about Ubuntu.