I'm referring more to the island greens that exist purely for the sake of it. There is one, #15 at the Tradition Golf Club, a piece of crap (in my opinion) just north of Pawleys Island. #15 is a 160 yard par 3 with a completely meaningless 'island green.' The green is very large--about 40 yards deep and 25 wide--with a couple big bunkers, and the edges of the island 10 yards outside those. It takes a full-out chunk or a shank to get the ball wet. The pond looks man-made, obviously a ploy to allow the club to say they have 2(!!!!) island greens (the other one is acceptable, albeit contrived, at #7). This I do not agree with. I actually anxiously await the first time I play #17 at TPC Sawgrass Stadium. As it is regarded as one of golf's most intimidating par 3s and the foremost island green, it is of interest (though I'll admit, some of my fascination is the resolution of whether or not it is an easier green to hit that #13 at Pawleys Plantation).
Here's why I don't think island greens are sensible on par 4s and 5s. On a par 3, the player is guaranteed (ideally) a flat, fairway-like lie. on a 4 or 5, it is probable that the lie on the approach will be less-than -ideal--be it a sidehill lie, or from rough. Depending on the size and severity of the island, this may be overly demanding, especially for the higher handicappers, who undoubtedly outnumber the good players. From my experience, island greens can be injurious to a sensible pace-of-play.
I'd be willing to concede that island greens are alright when done carefully, but I don't think they are good as a pre-fabricated "cool hole" formula.