My nephew and niece do. My brother and his partner aren't married so they gave their kids both their surnames. Pretty common nowadays I believe. But what's going to happen when all these Davies-Green's and Taylor-Jones' grow up, get together and have kids of their own? Bob Davies-Green-Taylor-Jones? Who has kids with Tracy Evans-Wilson-Roberts-Thomas and out pops Ian Davies-Green-Taylor-Jones-Evans-Wilson-Roberts-Thomas.
I do. When I married my American wife I added hers to mine (Duncan) as her father only had 3 daughters and I thought it give me brownie points. And now all my work mates think I am royalty lol.
A double-barrelled name is still an indicator of class. Once it was a sign that you were upper class, but now it is more common that the opposite is true due to unmarried parents. And of course there are the handful of liberal types that do it just to be different, or in the name of equality.