Problem 1: After upgrading to Jaunty, compiz couldn't be enabled.
The error was saying that the driver was backlisted.
To solve this create a file ~/.config/compiz/compiz-manager and put
Now enable compiz and it should work.
Problem 2: After upgrading to Jaunty, compiz is very slow.
You'll easily notice the performance degradation.
To solve this you can revert to intrepid driver by following https://wiki.ubuntu.com/ReinhardTartler/X/RevertingIntelDriverTo2.4
But what I did was used "UXA" instead of "EXA". UXA is new and far better but this has some bug, which prevented it from being default in jaunty.
To do this open your /etc/X11/xorg.conf and add
Option "AccelMethod" "uxa"
under Section "Device"