Mrs PixelMix and I got back from our New York honeymoon this morning, only 24 hours late. We were the first flight from Newark to be delayed (should have left Thursday evening) so BA stuck us in a hotel overnight and said we would be leaving the next day. We all clambered out of bed at 5am expecting to leave Friday morning, only to be told it would be Friday night. We were then told that there were no flights, but BA's own website confirmed that a plane was leaving for Prestwick (rather than the scheduled Heathrow destination). Unfortunately, BA HQ decided that rather than letting the Thursday night passengers know (as the local crew had expected and insinuated), the Friday night passengers would have their bookings honoured instead.
We had to rebook for a flight on the 22nd (a week later than expected) but thought we would try a lift to the airport and chance stand by just in case. Glad we did, as we walked straight on to the flight (most of the Friday passengers presumably thought it was cancelled or didn't want to go to Prestwick instead of Heathrow) and the plane left with dozens of empty seats. Cabin and local crew were furious that they were flying half empty when if it had been left up to them, they could have filled the plane with Thursday's passengers, most of whom are still in a hotel.
We count ourselves very lucky, as no idea when we would get back otherwise. At least BA are paying for hotels and food for non locals, but a whole week in a hotel in the middle of nowhere would have been a bit grin.
To cut a long story short, worth keeping an eye on the various websites and don't assume you won't get a stand by seat on any flights that do leave – in our experience, there is virtually no-one sitting in the airport. Ground and cabin crews have been incredibly helpful in difficult circumstances.