Vim: insert the same characters across multiple lines

Question

Sometimes I want to edit a certain visual block of text across multiple lines.

For example, I would take a text that looks like this:

name
comment
ph         


        

Answer 1

Updated January 2016

Whilst the accepted answer is a great solution, this is actually slightly fewer keystrokes, and scales better - based in principle on the accepted answer.

1. Move the cursor to the n in name.
2. Enter visual block mode (ctrlv).
3. Press 3j
4. Press I.
5. Type in vendor_.
6. Press esc.

Note, this has fewer keystrokes than the accepted answer provided (compare Step 3). We just count the number of j actions to perform.

If you have line numbers enabled (as illustrated above), and know the line number you wish to move to, then step 3 can be changed to #G where # is the wanted line number.

In our example above, this would be 4G. However when dealing with just a few line numbers an explicit count works well.