Your iPhone (or other iDevice) has but one button you use constantly: the home button. It has many functions, and as a result it's prone to becoming unresponsive. Designer Khoi Vinh has discovered that this problem is easily resolved with a little WD-40:
Title photo remixed from an original by Joshin Yamada.
As he explains on his blog:
In my experience, on not just my own iPhone 4 but also on my girlfriend's, WD-40 restores the responsiveness of the iPhone's home button to basically like-new condition. I just sprayed a little bit of WD-40 directly on the button, then pressed the button rapidly a few dozen times, tested its responsiveness afterwards, then repeated the process two or three times until it began to improve. Then I used the phone for a day or two to see how well the button did in actual use; I found that after a few days the problem ebbed back slightly, at which point I applied more WD-40. After the second or third application, the responsiveness remained indefinitely.
Khoi also notes that spraying WD-40 could possibly void your warranty. If you're concerned, contact Apple Support or head into an Apple Store before you give this a try.
The Miracle of WD-40 [Subtraction]