Jim Taylor covers a lot of policy issues pertaining to how Apple has locked down the iPhone. Read all about it here.
See intomobile.com and daringfireball.net's articles form more information. http://www.intomobile.com/2009/08/05/apple-censors-dictionary-app-forces-17-rating-claims-dominion-over-english-language.html and http://daringfireball.net/2009/08/ninjawords
See http://www.seankovacs.com/index.php/2009/07/gv-mobile-is-getting-pulled-from-app-store/#comments for more information.
As part of my ongoing blog post of why I won't buy an iPhone I'm recomending Will Geer's article Apple tries to silence
Someone put together a list of reasons an application could be rejected by Apple. Unfortunately Apple doesn't feel the need to share this information with it's developers. Read about it here