Casio GIEZ Ti-Rubber GS-300 Caliber 2301, ca. 2003

The rubber is still holding up after 10 years (November 2013)
To be honest, I expect this rubber band to deteriorate in the not too far future. For me, that is the biggest complaint with G-Shocks. Most of them have bands that are made for just that one model with specific lugs. Will Casio have replacement bands 10 years after the watch was released? I don't think so. Also, if the band is gone, you can basically toss that watch. Or use it as a mini wall clock or stick it somewhere on your boat or motorbike. Because the bands are often integral parts of the G-Shock cool factor, probably only very few will try to wear the watch with eg. a NATO or another replacement band.
Also G-Shocks often use rubber or resin on the watch head. That also limits the life span of the watch. See this example for a warning. This is one reason why I try to stay away from too expensive G-Shocks. With the "Twisted Metal" collection announced in October 2013, Casio has finally created some - albeit expensive- all metal G-Shocks that should hold up much better than the composite G-Shocks from the past