Here is a simple way to speed up the boot time of your Ubuntu system. It involves recreating the readahead profile. Readahead is a daemon that runs in Ubuntu that loads a set if files into page cache that accelerates the first time of loading of programs.
The initial install of the OS comes with its own default set of files. But every system is a little different and you can rebuild this profile in one easy step once you have every thing installed.
Your run this profile program once during boot-up, then after that you are set. I tested this out on a couple of different system and found that you can shave between 5 and 10 seconds off of the boot up time.
Here is how it works.
First boot your system. At the Grub prompt hit the 'esc' key.
At the next menu the default kernal should be selected, so hit 'e' for edit. Then arrow down to the line the starts with the word 'kernel'. Arrow all the way to the end of this line (after the words 'quiet' and 'splash') type the word:
Then hit 'enter' and then hit 'b'
Your system will then boot. For this first boot-up your system will take about twice as long as the profiling program sets up for the readahead. But after the next boot, you just bring the system up the regular way, and you will notice a little faster boot time.
This procedure is not something that I would do everyday, but if you install a new system, do a major upgrade, etc. then it may be helpful to run through this procedure.