Lubuntu is a derivative of Ubuntu Linux that uses the (extremely) lightweight LXDE desktop. Lubuntu is great on underpowered machines like an old netbook, and I currently use it as a virtual machine shell to browse Internet sites that may be of questionable content (mostly porn) and pose a risk of infection.
To enable automatic login in Lubuntu, you will need to install LX Session Editor. In terminal, execute the following command:
sudo apt-get install lxsession-edit
Once installed, edit /etc/lightdm/lightdm.conf with an inline text editor such as Nano. Edit the file to read as follows:
Reboot an you will be automagically logged in to your desired account!