Hi Bednobs.
I happen to know that Ed (filthiestfis) doesn't drive. While the IoW is fairly small, the limited rail system and the (ridiculously expensive) slow buses mean that a visitor without a car can only visit a small number of attractions in a day. If the weather's good, I'm assuming that he'll want to visit some beaches (and their local bars!) as well as visiting some of the key historic sites. You can't really do much in a day. Three or four days might well be enough for some people, but that depends upon how much time is spent on the beaches (or in bars!).
Chris