So, I upgraded to 12.04 and when I booted back up, my wireless keyboard worked fine on the grub screen, but as soon as I get to the log-in screen neither the keyboard not mouse worked. I swapped them out for wired USB ones, which also don't work. Any ideas what's up?
I don't know if this qualifies as an answer to your question, but I had the same problem and I solved it by upgrading further to 13.10. It was nasty for me because I had no PS/2.
I used a different system to downloaded Ubuntu 12.10 and made an install key. Then I booted my broken system off that 12.10 key. The keyboard and mouse worked, so I chose the upgrade 10 12.10. Once I upgraded and removed the 12.10 installer key, the keyboard and mouse stopped working.
But then I did the same procedure but with version 13.10. This time it worked.