It is a commonly held belief that Brett Lee traded pace for accuracy, but it is not strictly true. Lee came on to the scene as an 150kph bowler, who touched 160kph (not 100mph, but 160kph) in the 2003 World Cup due to the generally high speed gun readings - I think the explanation was thin air.
He then slowed down somewhat, after becoming more open in his action in 2005 (IIRC). In the 2005 Ashes, he was around 140-150kph, which is what he is now - so he didn't exactly slow down for accuracy - he has merely become more accurate. He may have even become faster in the Australian sumemr, as in the 2006/7 CB Series, he was in the low 140kph area.
The arguement of accuracy vs pace is an interesting one though. I believe that a bowler should, energy permitting, bowl as fast as possible whilst maintaining the action which they would walk through the action with. I don't believe that a bowler who sprints in with arms flailing and then points to gully before swinging the arm (Steve Harmison, anyone?) over has the right idea and this should be discouraged by coaches moreso than trying to bowl fast. Bowling fast with a reasonable action and being inaccurate is merely a case of inexperience and can be rectified with experience and target practice.