Have never worn a jacket on a NCL cruise. Just nice slacks and dress shirt. Except for formal pictures taken in the main lobby, never saw anyone in a Tux. The hand sanitizer stations seem to be keeping everything in check.
I haven't heard anything about the noro-virus however from experience the companies tend to manage this quite well with sanitising gel etc. Regarding the formal nights I would guess that at least 50% of guests (more if dining in the main Tsar's Palace Dining Room) wore dinner jackets, with ladies wearing evening trousers/skirts with sparkly/floaty tops, or cocktail dresses. However, in other restaurants the 'resort wear' attire seemed to be absolutely fine (we didn't attend the formal evening as it was not something our 14 year old son was comfortable with - we chose Cagney's steakhouse (cover charge applies) on the evening and had a wonderful time.
I was on the Jewel two years ago and there were two formal nights each week, majority of men wearing tuxedos, others dark suits, and ladies very well dressed in evening wear.
Just completed two weeks on the Jade and there was no dress code - more or less come as your are which spoilt the atmosphere of evening cruising. On Jewel no shorts allowed in public areas after 6 p.m. but on Jade anything goes.
We are travelling to the Baltic on the Jewel in August too (11/08 sailing). I understand that embarkation was delayed on the last Baltic trip by two hours in order that the ship be thoroughly sanitized. I believe passengers were encouraged not to shake hands and that all food was served by gloved staff-no help yourself buffet.As far as I am aware this has had a positive impact upon the virus.(we can only hope!) .