Macbook touchpad multitouch stopped working
Answer found on apple boards:

by Majicman in Nov 13, 2009 1:13 AM
I'm an Apple technician who works for a self-servicing provider. This happened to me today as well. Reboot didn't fix it, neither did a new user account.
Here's what I did that did indeed fix it:

Boot into single user mode. (hold down command + S on reboot)
Wait for the # prompt
Type exactly this: fsck_hfs -f /dev/disk0s2

When it's done, type shutdown -r now
Your Mac will reboot. Hopefully that fixed it for you, too!

For whatever reason I couldn't get into single user mode, so I just hold option and opened the Terminal there. Worked for me! :)
( I just wished I knew what the bleep disk0s2 has to do with anything here! )
Also, someone else mentioned there the fsck_hfs didn't work for them but this did:
/sbin/fsck -fy