I've had my SGS III for only a month, but, in that time, the button has the exact same feel & look as the day I unboxed the phone.
I'm sure someone may pop-in to report a defective button, & we'd like to hear about their experience.
However, from what I've read/seen around the various ANDROID sites, etc..., I've yet to hear about any problems with the home button, not a single article, nada.
SAMSUNG hasn't sold 30 million + of these phones by mistake, it's a solid piece of hardware .You can be rest assured that your phone will be just as solid of a choice. If a problem arises, you're protected w/a minimum of a one year warranty, possibly longer, depending on where you reside.