There is a lot to think about when releasing your iphone application as a free app, or a paid app to the App Store.
Here are 5 important points you should consider when deciding whether or not to charge for your application.

If it extends your current business to the iPhone (so the app does what you already do outside the iPhone).

If it’s stupid or unuseful, but funny (funny things are very appreciated by iPhone users).

If it might be potentially used by lot of people

If it’s not useful and complete, free things are generally considerated low-quality.

If it’s not a niche app.

iPhone app business model is not only based on selling the app. Consider advertising and derivate business like “selling something from your app” a good non-conventional strategy. Selling the app as free sometimes is better. As soon i’ll write something around unconventional business model with iPhone app

If a user comments on a post FriendFeed, the content appears on the stream of people who follow him. That content might potentially interest his friends, particularly because he liked the article enough to post a comment.

If friends of your friends also comment on the post, then even more people will see your content.
To see new comments, the user generally has to visit the blog, and sometimes they forget your blog address. If your comments are powered by FriendFeed, staying updated with the discussion means visiting the social network and not having to remember the blog address each time.

Viral promotions may take the form of video clips, interactive Flash games, advergames, ebooks, brandable software, images, or even text messages. The basic form of viral marketing is not infinitely sustainable. – Wikipedia