How to migrate core profile fields into the new profile fields in D7?
A good solution might be to use Feeds module (to import to fields) and Views Data Export Module (to export fields to the spreadsheet). The procedure would be:
  
  Setup a view that lists all of your users and displays all of the
  fields you want to migrate. Then add news display (data export) and
  choose CSV format.
  
  Use feeds to import the data to D7. Just map each exported field to a
  new field.
  
  This might seem complicated at first, but it's really simple and
  should work.


Thanks for your reply, take2. Thought it would be good to post it here.