Came across this link today
http://www.techradar.com/news/software/operating-systems/50-amazing-ubun...
Some useful (and not so useful) tips in there.
I have to try the bootchart one sometime:
'One of the best utilities you can install for checking your system's performance is called 'bootchart'. After installation and a reboot, 'bootchart' will create a complex graph of everything that's running and taking up resources as your system boots, and place an image of the graph in the /var/log/bootgraph folder.'