First off, you can enable profiling:
sudo gedit /etc/default/grub
replace GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash” with GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash profile”
save and exit
sudo update-grub2
sudo reboot
after rebooting:
sudo gedit /etc/default/grub
replace GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash profile” with GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash”.
save and exit
sudo update-grub2
You may find something on the internet about "CONCURRENCY". Adjusting this value is obsolete in 12.04
There are more tips and tricks at http://georgovassilis.blogspot.com/2011/05/speeding-up-ubuntu-1104-boot-time.html, if you want an example of getting into bootcharting. This is different for each system, though.