Condensed iOS Human Interface Guidelines
Imperatives for AppStore approval
For iPhone app developers. Emphasis on getting the fastest app store approval. Everything stated as suggestion made into an imperative. When "violating" these imperatives, you can check for yourself what the caveats are. Generally speaking, deviating will more likely cause your app to be hung up in approval.
You can read this entire document in about 20 minutes. This is faster than reading and understanding the entire Human Interface Guidelines.