I tried reading them on the ticket machine a Victoria Coach Station once, I was skim reading quickly because I was in a hurray and before you even get 1/3 of the way down the stupid thing decides you have taken too long and cancelled the purchase - now tell me how the heck I'm supposed to buy a ticket when in order to do so I have to answer "yes" to the "do you agree to the T&C" question?
I gave up and stood in the (as usual) very long queue instead.
I always read insurance documents and financial agreements at least 3 times over at least 2 days, otherwise it depends on what information/ rights I think I am giving up, the size of the transaction, my feelings about the company and if whether or not I have prior experience of them. For example I a, far more likely to read them if its a 12 month phone contract with BT than I am if its a PAYG sim with GiffGaff.