I don't see any danger in offering "advice" whether it be medical or legal or computer as long as you don't misrepresent who you are. (In other words I don't even think you have to say IANAL you just shouldn't represent that you are if you are not.) Why? There should always be a general degree of caution and since there is no way to verify that someone is a lawyer or doctor (with a few exceptions such as grellas who openly posts contact info) the assumption should be that the advice is strictly to point you in the right direction and you need to pay someone in the end).

With regard for the reason for this "Ask PG" IANAL but I have plenty to say about this by virtue of the fact that I own domains and have successfully fended off Fedx and American Express as well as several other smaller companies. In some of those cases I've used an attorney and in other cases I have not. What I think about this does count even though I'm not a lawyer. Lawyers also keep in mind know the law but they don't think strategy many times which is also important.

As far as "liability" I think you are taking this to seriously. Do you really think someone is going to bring a cause of action against someone writing something on hacker news with the appropriate disclaimer (or not)? Why not a cause of action if someone gives bad advice on a backup solution? That's going to hold up in court? While anything can happen I think this is extremely remote. A comment on HN is not like writing a blog and pretending to be a lawyer.

Above opinion by the way is based on my 30 years in business avoiding all sorts of legal issues along the way.