This complaint was first posted June 26th 2010 and here we are 25th of August 2010, now with version 4.0.2 and it still sounds like I am down a well with a pillow over my mouth, whenever I use the bluetooth in my car. My customers cannot understand a word I say. Calling apple support and letting them know that you have this problem, gets the response, "Yes, we are aware of the problem, we have been recieving many calls about it." At least they are not denying there is a problem, now they just have to hurry and get it fixed.
If you haven't called the apple support line yet, do it now. It is the only way to put pressure on them to HURRY.