From the UltraEdit manual:

**************************************************
Column Mode

This command changes the operation of the editor
for selecting text.  When column mode is selected
highlighted text is based on the character column
position of the first character selected to the
column of the last character of text selected. 
Text selected in this mode does not automatically
include all text between the start and end
position, but includes all text in the columns
between the first and last character selected. 

Column mode editing is sometimes referred to as
block mode editing as the act of selecting text
forms a rectangle. 

Cut, Copy and Paste work with the selected text. 

Column mode editing requires the Word Wrap be
turned off and a fixed pitch font be selected. 

When column mode is enabled, additional column
features are enabled; Insert/Fill Columns, Delete
Columns, Cut Columns and Insert Number. 

Shortcut Keys: ALT+C   
**************************************************

Full block mode editing support is, in my opinion,
 one of the features of UE that sets it apart from
all other editors. As gedit seems to be getting
much inspiration from UE, it would seem fitting
for it to also support column mode. 

Skeptical of its usefulness? Consider the
following examples:

Example 1: 
I was recently working on writing some queries for
DB2. After writing ~15 queries and starting to
test them, I realized that DB2 requires a
backslash at the end of every line. In a normal
editor, this would be quite a pain. However, with
column mode, I simply selected the column I wanted
 and hit the backslash key ONCE. Much easier with
column mode!

Example 2:
I've got a 50 line block of text that I realize
needs to be indented in order to be wrapped in an
if() condition. In an ordinary editor, this could
be a real pain. With column mode, I simply select
the first column of the next, and hit spacebar 3
times. That's it!

Example 3:
I was recently editing a log file which contained
timestamps in the following format: [hh:mm:ss]

The target application required the format to be:
(hh-mm)

The log was ~10000 lines long, so changing all
these timestamps could be been a horrifying
problem. However, with column mode all I had to do
was select the column containing the first '[',
then hit '(' ONCE to replace all of them. The ':'
and ']' were replaced the same way. Removing the
':ss' was as easy as highlighting those 3 columns
and hitting Delete. Done!



If anyone wants more information on column mode,
either try it out on UltraEdit (Alt+C, or
'Column-->Column Mode'), email me (blueeskimo at
gmx.net), or msg me on IRC (#gedit on
irc.gimp.org, nick EsKi).