By enabling dash as the default shell, I shaved 1 second of the boot time. This isn't much (5%), but still remarkable for such a small change.
How to enable it?
install dash: apt-get install dash
make dash the default shell: dpkg-reconfigure dash, and answer yes if you want dash to be /bin/sh.
Bootchart with dash
Just to be sure, I'm also attaching my bootchart.