Randomly and fortunately not too often (maybe two or three times in the last 5 months) the mouse cursor freezes on my laptop (Ubuntu 11.10 64Bits). This usually happens when using thunderbird, however I don't have a test-case to report to launchpad yet.
This is quite annoying and what I did in the previous occasions was to hit CTRL-ALT-F1 and restart lightdm.
However It has just happened once again right now, so I did a quick search and I've found a clean workaround to bring (activate) the touchpad again. Simply launch a terminal (ctrl-alt-t) if you already don't have one at hand and execute:
Credits to effenberg0x0 from ubuntu forums.
Synclient (from it's man page): is a program that lets you change your Synaptics TouchPad driver for XOrg/XFree86 server parameters while X is running.
man synaptics man synclient