With Grub 2, you can change the default menu entry without changing order by editing /boto/grub/grub.cfg. Edit "set default" line to be of the titles in /boot/grub/grub.cfg.
But in Ubuntu/Debian, you want to edit /etc/default/grub and change the appropriate line there, then run "update-grub".
In Unity, there is no easy, risk-free way of changing Unity settings. You can install Compiz Settings Manager but that will make baby Jesus cry:
I am an experienced Linux user, I've contributed to kernel and work on the Canonical OEM team; I only mention these facts to show my context, which is -- the other day, I did a fresh install of 11.10 on my laptop, and wanted to customize something (turning on focus-follows-mouse). I poked around in gnome-control-center for about 30 minutes before giving up and discovering the only way to do this was using ccsm.
After installing ccsm, I configured ffm, and then -- accidentally! -- my mouse cursor passed over the preferences button and the touchpad on my laptop registered a click.
Boom!
Unity session dead.
Holy crap, what a crock.