I never have, though in college (97-01) I would occasionally do the adidas pants if it was an earlier class.
But after that, not really. I feel sloppy. On planes I've learned to opt for leggings and some sort of tunic/sweater dress.
Here, I kind of like how people look more put together on the weekends. In the US, the malls seem to be plagued by the girls still wearing the Juicy suits, or the Pink sweatpants from Victoria's Secret. I feel like people need to make SOME sort of effort, I don't care of the sweats are designer!