In reply to dirtbag1:
No yr probably right. I should have expanded a bit more but I was feeling lazy when I posted.
So, I don't go completely straight and lock my elbows off, cos as you say, thats likely to lead to injury. However, I drop to nearly straight, keeping a small abount of tension in the elbow. Then when I do the pull up, it helps strength train throughout the whole cycle of arm movement and not just the last 90 degrees.