Ubuntu has a laptop-mode-tools package, which is installed by default on laptops. However, laptop mode is disabled by default in Ubuntu Edgy (6.10), because some people have been experiencing hangups with it on certain laptops (mostly Thinkpads). Until now, nobody has any clue what is happening here. To reenable laptop mode, edit /etc/default/acpi-support and set ENABLE_LAPTOP_MODE=true.
If you want to use the latest version of laptop mode tools, you can use the Debian packages, they are compatible enough to work out-of-the-box on Ubuntu. In fact, I would definitely advise using these packages -- the Ubuntu packages are crippled so that some options don't work, the most notable of which are ENABLE_LAPTOP_MODE_ON_AC, ENABLE_LAPTOP_MODE_WHEN_LID_CLOSED and DISABLE_LAPTOP_MODE_ON_CRITICAL_BATTERY_LEVEL.