They don't stand the whole night, just most of it. There is a dinner component, and usually someone sings a couple of songs afterward, but mostly it is a cocktail party, socializing on your feet. No sititng in theatre seats, so you can sweep the train of the dress to the side of your chair at dinner.
Lupita Nyongo's dress was lovely (if you scroll down the page on that linked site, you can see the rest of it. Just a plain sweep of silk chiffon chemise with hand-sewn rectangle paillettes on it. Nyongo is very astute about what flatters her figure; she is built like a model 1920's flapper, simple lines work best for her.)
The feather gown Saldana wore was a masterpiece of the couturier's art, which is what this event is really about. (There are several close-up photos of it on the Daily Mail site:
http://www.dailymail.co.uk/tvshowbi...a-gown-feathers-elongated-train-Met-Gala.html.) That one would be nearly impossible to sit in in a conventional chair; the designer probably arranged for her to have a stool-type chair at dinner, so that the skirt could be dropped over it (or she removed the skirt entirely, which is a good possibility; in the closeup photos the skirt looks like it might not be attached to the bodice, it had a satin sash tied at the back.) FWIW, that gown was a brilliant move on the part of D&G; they are currently being boycotted by a lot of celebrities, and I'm sure they meant to use it as a statement piece to remind those folks why it pays to wear D&G.
The true "spotlight" went to Claire Danes, actually. The theme of the night was
Manus x Machina, and as usual, many of the designers tried to go with the theme of futurism and robotics. Danes' dress was the embodiment of the theme, though you couldn't tell in the red carpet photos, because it was still daylight out. The dress was LIGHTED. Look at the inside-the-gallery photo from CNN to see the effect:
http://www.cnn.com/2016/05/02/fashion/met-gala-2016/index.html
Gaga seems to have forgotten her skirt entirely.
FWIW, I am dying to see that exhibit. I haven't been to NYC in ages, but I do believe that I'm going to manage a trip this summer. This show is a dream come true for people who love to sew. If you are interested, here is the Met's promo film for it:
http://www.metmuseum.org/exhibitions/listings/2016/manus-x-machina