We just did a B2B on the Elation in December (our first). Unfortunately we did not book both legs at the same time and had to change cabins. Not a huge deal, but we did have to pack up and ask our room steward to take our luggage to the new cabin. We just kept the luggage in the cabin and he got it moved for us.
We were also sent a letter to come down at 10:00 am. By 9:15 the ship was cleared of all other passengers so we went to the Atrium Bar and sat down in full view of the service desk. At 9:30 a customer service rep rounded all of us up (about 4 or 5 couples) and walked us off the ship, and through customs. She then handed us our new S&S cards and walked us back on the ship. We had to come back at 11:00 to get our pics made and our credit cards swiped to activiate the S&S cards since the photog's were not set up yet. It was a pretty smooth process, and would have been much better had we not had to make a cabin change.
We were also concerned about seeing the same shows twice, but the big show "Win" that was supposed to be done on our last night got cancelled due to extreme rough seas, so we were glad we saw it on the first leg. We did get tired of eating though.
Been there - done that:
2005 Holiday, Sensation, Conquest,
2006 Conquest, Celebration, Holiday,
2007 Freedom Grand Med, Holiday
2008 Fantasy & Sensation,
2009 Fantasy, Holiday & Dream Grand Med
2010 Fantasy and B2B Elation
2011 Monarch of the Seas
2012 Booked - Breeze from Barcelona 12 days