Brother may make some of the ugliest printers on the market today, but I love how friendly they are toward Linux users. I ran into only one obstacle while setting up my HL-2070N as a network printer, and that wasn't their fault.
The LPR and CUPS (wrapper) drivers are available for download from the Brother Solutions Center. Since Ubuntu uses the Debian package management tools, I chose the Debian LPR driver and CUPS wrapper driver. The instructions Brother provided were clear and concise.
dpkg -i --force-all brhl2070nlpr-2.0.1-1.i386.deb
dpkg -i --force-all cupswrapperHL2070N-2.0.1-1.i386.deb
Ubuntu includes the LPR and CUPS packages, so I didn't need to install them. However, I had to make some slight configuration changes because Ubuntu expects you to set up your printers via the GNOME Print Manager. I'm accustomed to the CUPS web admin tool, which is disabled by default under Ubuntu. To enable it, the cupsys user must be added to the shadow group.
adduser cupsys shadow
Note that you need superuser privileges for the above commands to work. Speaking of which, here's how to enable the root user in Ubuntu:
sudo passwd root
Now the only thing left to do is add the printer. Point your web browser to http://localhost:631, where you should find an entry for the Brother printer. For the moment, it's probably configured for a USB connection; that seems to be the default. Click "Modify Printer". The settings you must change are the device and the URI. For device, select "LPD/LPR Host or Printer". For the URI, type lpd://nnn.nnn.nnn.nnn/binary_p1 where n is a digit of the printer's IP address. (You should assign a static IP for the printer.) When you're done, CUPS will prompt you for a username and password. Use root and whatever password you've set.
That ought to do it. Enjoy your network printer!