We are a startup about to soft launch our app within the next month on iOS. We are currently bootstrapped and will launch very quietly for a few months as a public beta. Eventually we would need to incorporate, but who knows when. Do I need to form at least an LLC since we will be public? There will be posting from external sites onto our app, and we want to limit liability from that. Also, the app is focused on interaction between strangers and we want to limit liability from any issues that can arise with that. But once again, our initial goal is to launch very quietly and try to get to just a hundred engaged users.
As lawyers have jumped in already with lawyerly advice, I'll offer you a different perspective to your question. Apple allows two types of publishers into the app stores. Individuals and Corporate Accounts.
Corporate Accounts require a Dun & Bradstreet number which of course, require a corporation to be formed in order to get a D&B number.
Transferring an app from an individual developer account to a corporate account post release in the AppStore is a bit of a pain (they require you to prove you are a founder / cofounder of the company you are transferring to) and depending on the kind of app you're building, a corporate presence might make an incremental impact in the user trust of the app.