That's not the same as what he's got here...
I think this is pretty neat. I like remove_columns especially. I
don't know how much I'd really use add_columns, but having it like
that would be nice just in case. 
--Jeremy
Why not DRY it up even more?
columns "users" do |t|   t.integer :group_id, :employer_id   t.string :first, :last   t.timestamps end
You know exactly which columns are being added. Reversing the migration should be able to use that structure to automagically remove the columns.
The catch would be if there is additional processing occuring during the migration which would need to be reversed during the back-out.
cheers
