It amazes me that with all the "antennagate" stuff, with the original iPhone 4, the Verizon iPhone 4, and now the white iPhone 4, there has been to my knowledge only one site that actually investigated the problem correctly. Anandtech is the only site I've seen that actually looked at and compared the signal attenuation in decibels, rather than using essentially meaningless "bars."
Does no one know about field test mode? It's really simple to get to and gives a much more quantifiable answer to the existence of any antenna improvements.
For those interested in Anandtech's original articles for the original and Verizon iPhone 4.
http://www.anandtech.com/show/3821/iphone-4-redux-analyzing-apples-ios-41-signal-fix
http://www.anandtech.com/show/4163/verizon-iphone-4-review/2