I too just got upgraded to a B3 cabin. I couldn't be more happier. I booked the lowest inside cabin. This is a huge upgrade. I feel lucky that I'm going to have a balcony. I'm sure you'll beable to see some water. If you were originally booked in a inside cabin, I wouldn't use the term "misfortune". It's a "good thing. BTW I'm on the April 25th sailing.
When I received my documents I noticed my cabin # was different then when I booked. I'm not sure why I got an upgrade? I've never sailed with Cunard before. It could be I booked the tandem crossing almost 2 years ago and paid not much less than full fare. Sometimes Lines will sell lower cabins at a discount and passengers who paid more will get an upgrade.