Yep, all 4 do it. The problem with it is that my husband and I both have black desk chairs....it is hard to see the black cats.... more than once they have been sat upon. Not very happy about it either!
Mik does it ALL the time... so much so that it has become a game of sorts. Not only does he steal the computer chair, he steals my spot on the futon or sprawls on the bed as soon as I get up. He's so cute when he does it though that I can't resist telling him it's working in his favour.