Unfortunately, the clunk affects 2003- 2007 AND, even the 2008, as I have come to learn. The Clunk is felt when you are slowing down or when you come to a stop, 1-2 seconds later, you feel a lovetap or a slight "clunk" from the rear. There's a technical service bulletin for this from Lexus and they will change the driveshaft and control arms for 2003-2007. As far as I know, it's just an annoyance and no safety implications.
can you get the drive train replaced even if you arent experiencing the clunk? i.e. can you tell them it happens intermittently?