I've noticed that people post bit.ly links quite often. I don't notice it as often here as the other SE sites, but it's still a problem, in my opinion. There is no reason to post a bit.ly link at all. Should we be discouraging these links?
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.