Well, for 2010/2011, you can't compare a 7 night SUMMER caribbean cruise. For example - our 2011 7 night Western in Oct is $3622 for Cat 7A secret verandah (well, we paid 10% less because we booked on board, but it's still listed the same price now) - 2 adults, 1 child. That is off season, so cheaper. The June 16 2012 on the Fantasy 2012 for cat 5E (so a little higher category) is ~$4300. I would expect summer to be more, because in July/Aug, it's even higher (like $5100).
HOWEVER, we did a 5 night DD this past Aug on the Wonder. Before we got FLR rates, it was $4900 for 2 adults 1 child in a Cat 7 (secret verandah) -- that is what we booked it as (FLR took it down to $2600!!).
To me, $4300 for a 7 night Eastern on the Fantasy in 2012 is much better than a 5 night for $4900!!!