The worst area seems to be JavaScript, since that world is full of trendy new options. The most common one I see here is where someone wants a solution to a JavaScript problem and gets a JQuery response; even though a JavaScript solution would be trivial and the OP's not mentioned JQuery. That has a tendency to push people into using libraries where they're not required.
For .Net questions most of the issues seem to be in the ORM space; i.e. the boundary between .Net and SQL; where people asking for help with SQL are pointed to LINQ, and people wanting to do database-first are pushed towards code-first solutions.
It's not really an SO problem (or at least not a problem that I can think of an easy way they'd be able to solve); more there are so many solutions and no best way; and giving the full context of the developer's experience, preferences, and situation would take several essays, then matching that to those qualified to supply a suitable answer for that particular scenario would require really intelligent filtering; assuming that such people exist and are active on SO. So the current solution of having lots of answers to pick from, and allowing people to up-vote and comment to help remove bad answers and help show which answers are the more generally preferred (thus driving those who don't have a preference to follow the general consensus and thus move towards some form of standard approach within the community) seems a pretty good one.