claus - 11:19 pm on Feb 25, 2010 (gmt 0)
If you make a 301 redirect, say from B to A, then the user will never see the page on domain B. S/He will be instantly transferred to domain A.
So, WRT. "it leaves the original content in place" this will not matter at all.
As for what to do, a page-by-page redirect strategy is always better than redirecting a specific page to the root of another domain.
So: Always redirect an "old" page to the same page on the new domain.