I just installed 9.04 release on my Acer Aspire 5500 and all was ok except the touchpad.

If you want it back, follow these instructions (in a terminal) :

sudo  pico /etc/modprobe.d/psmouse.conf

Add this line in the file and save (CTRL-O / CTRL-X):

options psmouse proto=exps

Reboot or try the new setting with :

sudo modprobe -r psmouse && sudo modprobe psmouse