When I got my iPhone from Posterous, I went into panic mode about accidentally scratching it. I went to Wal-Mart and bought an Incipio case which included a screen protector and a heavy duty black case that was very bulky. After I heard about Default Case, I thought it was too good to be true. I ordered my $0.01 case, a "Glorious Green" one, and waited a few days. The experience was awesome. Not to mention, the price was about 1/5 of the price that I paid Wal-Mart for the Incipio case.
DefaultCase has been engineered with perforations (pretty little holes) specifically to improve the reception of the iPhone 4. These holes allow the cellular signal to escape while preventing your skin from making contact with the iPhone's external antenna. This means fewer dropped calls and noticeably faster 3G/EDGE downloads.
So, what do I know? I just know that I like it and that people I've shown it to really like it. I tried it out and didn't know if I could trust the company but I must say, it's been a good experience. They explain their logic in their FAQ, for anyone interested.