Questions about the dd command

[elmo]

I've spent literally hours trying to find direct answers on the dozens 
of websites that discuss 'dd'
but the couldn't find what I wanted.

A few questions about the ' dd ' command:

  For example:     sudo dd if=/dev/sda2 of=/dev/sdb2 bs=1440

  1. Which is preferrable;    execute the command from an installed
       ubuntu (/dev/sda2) or from a ubuntu CD?

  2. How do you  modify the example  to show the data as it is being 
copied? 
     Would this have a drastic effect on how long it takes to complete 
the copy
      compared to just watching a blinking cursor?

  3.  What effect on the does the ' bs = ' number have on
      the time to complete the copy or the accuracy of the copy?  Is 
there a
      default number if the the bs=    is omitted from the command?