I upgraded to Ubuntu 14.10 today. It was mostly quick and easy, except my Dell XPS13's touchpad stopped working after the upgrade -- the hardware wasn't even being recognized, and it didn't appear in the output of
xinput. It turns out this was a result of the kernel upgrade from linux 3.13 to 3.16.
After some playing around, I found that I needed to unblacklist the kernel module i2c_hid (by deleting the file
/etc/modprobe.d/blacklist-i2c_hid.conf). Then, after either restarting or
modprobe i2c_hid, the trackpad was recognized again. I suspect that had previously blacklisted this module as a fix for some touchpad issues in a previous kernel; a quick search indicates it's a fairly common suggestion for touchpad problems.