Either you hate it, or you love it: Line numbers in the Eclipse Editor:
Personally, I love it!
Not every Eclipse distribution has it enabled by default (CodeWarrior 10.2 or later has it on by default). In case you want to get the extra screen real estate, or to change the setting, here is how to do this:
The setting is under the menu Window > Preferences > General > Editors > Text Editors:
If you don’t know where there is a setting, simply type in a word in the ‘filter’ text box, and Eclipse will show all settings which could be related to it: