We're still living in the "big family house" but plan to downsize at some undefined point in the future... probably when the cleaning and maintenance become too physically demanding. For now, we like it here quite a bit, and we can handle it financially and physically.
Current living space is just over 4500 sqft. This includes a 530 sqft detached guest house with full bath and kitchenette. Main house is 4000 sqft... 2 story, 4 bedrooms, 4.5 baths. There's also a 625 sqft "barn"/storage building, which is not included. This all sits on 2.2 heavily-wooded acres with a pool, deck, and a large pond that we share with a few neighboring properties. It's going to be hard to leave this place, but we will eventually, as it's completely impractical for the two of us.
We also have two rental houses, one of which might become our downsize house. One is 1100 sqft, 2 BR, 1 bath, 1 carport, with a large yard. The other is 1800 sqft, 3 BR, 2 bath, 2-car garage, with a very small yard.
Our dream house is ~2300 sqft, 2 BR, 2 bath, huge kitchen, great room, on 1 acre, atop a hill with a view in the Texas Hill Country, along with a 1000 sqft woodworking shop. Not sure that would count as "downsizing" though.