I don't know exactly when the policy of allowing casual dress on the last evening of a cruise started but it was in effect in December 2010 when we cruised on Mariner from Cape Town to Ft. Lauderdale. Frankly, I doubt I've seen more than a couple of people wearing jeans on the last night of the three cruises I've been on since then. IMHO, we're making a mountain out of a molehill. It's not a problem now, but the best way to guarantee that more people will start wearing jeans, etc. on the last night of a cruise is to keep discussing it on public forums. In this case I think the best policy is to let sleeping dogs lie.