landing CA and timeline

The Buffalo office has notified me of the approval of my application for CA PR, asking for passports. Now it is time to plan the landing matter. From this newsgroup, I notice that many have landed Canada and successfully returned to US without applying a visa, but the information I have collected (from website and company lawyers) so far suggests that a new visa is necessary for US reentry. Does this really depend on the boarder officer - a matter of luck? Can anybody shed some light on this topic?

The following is my timeline just in case you are interested:

=>Application submitted (from US) at the end of October 2003
=>First letter (file no) received in the first week of November 2003
=>Second letter received in early June 2004, interview waived, medical examination performed, and updated documents sumbitted in the same month.
=>Third letter received requesting passports on October 29, 2004.