When I switch from working with Delphi to working with Perl I miss autocomplete and gui form building (and the fantastic white-on-black colour scheme), but Jedit (www.jedit.org) eases the pain a little. It is Java-based so would likely work on Ubuntu (I run it on Windows and OSX). It has some useful plugins available for Perl development, like PerlSideKick, which shows all the subs and used modules in the current file, and Console, which can be docked in the window so you can get to your shell easily.
How can you feel when you're made of steel? I am made of steel. I am the Robot Tourist.
Robot Tourist, by Ten Benson