Well, I did have a small amount of frost around the opening of my sleeping bag in the morning, but if I had cracked the weather shield snow would have blown in. That was some serious wind with gusts that must have been around 40 mph.
No snow blew into the pockets, but this may have been due to the Snugfit. Velcro matches up, so the underquilt made a full-length seal at the top edge of all pockets. Don't know if this would always keep the snow out, but it worked in this case. Attaching the underquilt this way makes it tough to use the side pockets for storage, but I guess you can't have everything.