That's fine for startup-ish hires, but in most of those cases, isn't the candidate being sought out/referred/etc? Almost all of my work is on non-public SCM systems, and frankly, my job doesn't leave a ton of time to post to *overflow sites, and when I go home, I'm home, and spend it with my hobbies and family.
I also consider myself a really great developer. Especially in the more corporate .net world. When I review candidates, I find that a simple (at a PC, with resharper installed) coding test, with a prebuilt solution, needing only an implementation of a method done, is a great filter for competency. And after all, rough competency is the most I hope to get out of a coding test. The far more important part is always the stuff like how well I think they'll fit in a team, how their approach to solving problems in general is, etc.
Syntax memorization is no longer a measure of a good developer. All it shows is basic competence in a language.