1----SkippersMom, I think Kuki's theory is true about 1st timers getting upgrades. I have seen that a lot, but more so in the past.
2----Also very true that a guarantee booking is much much more likely to get an upgrade than an assigned cabin.
3----The latest trend I see is: Many more upgrades are given to bookings made through Travel Agents. Not the mega-online TA's, but standard TA's. I think TA's have complained to the cruise lines about this in the past and the they have responded. I have heard or read a lot of this of late.
Hawkeyes observations are 'right on' too.