Marco Arment,

According to Apple, apps that feature an embedded web browser or provide access to 3rd party content also automatically require the 17+ rating, regardless of the application’s content or intended audience.

It means that (1) all Internet applications (say, Twitter clients) need to tell buyers that they contain frequent nudity, intense profanity, and drug use, and (2) no more promo codes, which prevent developers from easily giving free copies to reviewers.

Marco even has serious doubts about the viability of running a business selling iPhone apps.

UPDATE: Promo codes are allowed again.