I believe that the iPad is a great medium for a magazine. But, most of the current offerings in the app store has got it all wrong. I don't want a iPad magazine to look like a adventure game, often the layout is to confusing and many publishers try to cram in as many "multi media" functions as possible. A iPad magazine should be similar to the printed version with sparse use of rich content where it adds value to the article. Good examples of successful iPad magazines is the British car mag EVO and the Swedish daily "DI+", poor examples are "The Project" and "Wired" (messy layout and to much rich content).
Also, untill Apple does something about it's pricing in the app store the magazines will be to expensive to really take off...