If you are using PL/SQL Developer as much as I do, you may be using the column editing mode. Press the Alt-key and drag your mouse to select some text. Now you can use a couple of options (like copy, cut and paste) on your selection. For instance, use the indent option to move you selection.

I have created a plugin to mimic a bit of UltraEdit, now you can use two options: add to selection or replace selection. You can download this plugin from my site.

It installs the following menu-items:
Edit / Selection / Column Edit (Replace)
Edit / Selection / Column Edit (Add)

I hope you enjoy the use of this plugin as much as I do.