Not seen it since I was at school - one of our English teachers was obsessed with Beckett and put on loads of his plays. If you've not seen Krapp's Last Tape performed by a 16 year old boy you've not really seen it at all.
Yes, booking was actually surpisingly easy (ironically, Facebook reminded me today of a selfie I took with Daniel Radcliffe 2 years ago - I know, I know...) I guess booking tickets to Lungs may be a more traumatic experience.
Don't remember it being that hard to get tickets for Matt Smith in "Unreachable" or "American Psycho" although in both cases I think they announced his casting after booking had opened. Claire Foy may be more of a draw?
This is definitely true in the case of American Psycho and I don't remember it not being true in the case of Unreachable. The Old Vic is a fairly large theatre though, so it's easier than the Almeida or Royal Court in numbers terms if nothing else.