Remember the tag was only put in place to help search engines in the first place. (Well, to stop people from spamming to get good search engine results. I think you get my point.)
So yes google can disregard nofollow on a case by case basis and face the associated potential legal consequences. I am sure that this would not be a problem in the case of stackoverflow, but I am not sure this is true in general.
As such, I don't think nofollow could have any possible legal consequences. It's intent is to indicate that you haven't vetted the links in question and as such are specifying a lack of trust in their content (i.e., user-submitted links); though like the article says, many people attempt to micromanage SEO through them which dilutes their usefulness (I've been told we have some links that do the same thing; no doubt someone thinking they were smarter than Google... so now we have to track them down and undo these pointless additions)
"You can browse my pages but you can't get useful information from them" is bizarre. I'm not saying that no site anywhere will ever sue over it, because this is America and you can sue over anything.
This is somewhat correct. While Google won't disregard noindex/nofollow directives (or robots.txt Disallow) it can - and will - show "blocked" pages in SERP if
the quarry is specific enough or a the page is "strong"
(lots of inbound links/strong social signals and etc...)
However, it will not show in page info (hide description and title) and use alternatives sources of information to fill those out instead.
For example: it can use DMoZ info instead of the real one.