A massively interesting read over at Anandtech. In my mind its the tech/geek site that has transplanted arstechnica as the real champion of full on tech geekiness as the latter has become a gadget site. Anand Shimpi has posted his review of the iPhone 4. The entire article is worth a read. But I want to point out one interesting section (in the beginning) where he basically reveals why some people have reception issues and some don't (I personally didn't) and that in fact both types of people may be seeing signal attenuation.
It all has to do with how the phone bars are defined. What does 1 bar mean on an iPhone or any phone? The best signal a phone could ever receive is -51 dB. The worst signal before you lose all reception is -113 dB. The iPhone defines it's bars as such
0 bar <=-113 dB
1 bar -107 to -113 dB
2 bar -103 to -107 dB
3 bar -101 to -103 dB
4 bar -91 to -101 dB
5 bar -51 to -91 dB
Note the large band for 5 bars. You can probably see where I'm going with this. Shimpi found the worst case drop in touching the phone in a particular way was 24 dB. Look at the chart below. It's a schematic of the actual size of the bars in the -113 to -51 dB spectrum (the white boxes). Below that are 4 examples of a 24 dB signal drop (yellow boxes). You start at the right of the yellow boxes, touch the iPhone inappropriately, and end up at the left side of the yellow boxes . A 24 dB drop can translate into all manner of bar drops depending on what kind of signal you are initially receiving. Are you very close to a cell tower? Then you'll probably see no drop in bars. Have a weak signal? Then you'll see multiple bar drops. Great stuff.
Effect on phone 'Bars" due to a 24 dB drop in signal