I agree, bit.ly links in questions and answers are pointless and are somewhat harmful - you can't see where the link goes without clicking on it, and it both relies on and provides information to a third-party service. I suggest that all URL shortened links in questions and answers be rewritten with the full URL.
As for comments, there is a character limit, so a shortened URL might be used to stay within the number of allowed characters. This is the only case where bit.ly or other shortened URLs should be acceptable.