I have an iPhone 3GS and have used the "disposable" screen protectors where the bubbles are impossible to get out. The wet application of skinomi ensures that it is completely bubble free the first time.
Application - after cleaning my iPhone thoroughly, and being really careful with following the instructions (clean hands, wet fingers with solution, apply on cleaned surface, allow a day to dry). Somehow, dust still got in between the screen and protective film. And I did not know that it was there during the wet stage, since the screen has a rainbow effect while it's wet and I wouldn't be able to tell. Once dust or anything sticks to the adhesive, it's over. I tried to peel it off, clean it, and re-apply and the same dust is still there. I thought I would be able to live with it so I gave it a few days. But it got annoying and really visible with white-lit backgrounds that I ripped it off and threw it away.
Conclusion - this is probably the best protective film on the market, but it was wasted $10 for me. iPhone screens are pretty scratch resistant, and you can't beat the original glossy feel and responsiveness of the bare phone.