I always tell the truth, if I was asked I'd spill my guts. But at the same time if we're talking about long term reprocussions from telling to truth, I'd rather not fuck up my life cause a mate chose to fuck up his. If I found myself on the other side of the situation, I'd want my mates to do as much as possible to help me out, but without stringing them selves up as well. After all if I did punch that old lady (hey she started it!) it is my fault and I have to live with the consequences of my actions and I'd expect my friends to do the same.
Society especially in regards to the growing litigious nature no longer seems to think that people need be responsible for their own actions. If I tripped over an uneven bit of paving, I believe it is solely my fault for not watching where I was going as opposed to the councils fault for not making it flat. At the same time, if I took way too many drugs and got myself into such a state, it is my fault for going too hard at it and thus my fault for anything that should arise from being in such a state.