[Spangles Muldoon]

In my opinion, the point of the exercise is that you write down negative/ unhelpful thoughts as soon as you have them so that you can challenge them immediately. If you can be bothered to start up a computer everytime you need to record something, I think it would be fine. When I did CBT I carried a notebook everywhere because it was easily accessible.
As you say though, it's probably quicker typing it out.

This answer is perfect, because it recognizes the major purpose of recording one's automatic thoughts.

The excellent book Managing Social Anxiety, by Hope, Heimberg and Turk, states that the client should record his or her automatic thoughts "when cognitions are fresh: (a) When anticipating a situation, or (b) As soon after a situation as possible." Long after the situation, we tend to repress, de-emphasize or recast our automatic thoughts in light of a mental attitude quite different than the one we had while the anxiety-provoking situation was being experienced.