"Wow, this is getting more and more complicated. And to think I started out just trying to add a few features to the forum. :)"

Sorry..

"The idea of an optional online test to establish knowledge level is interesting. But aside from the possibility of people answering the exam with a book in their laptop (or 8052.com or the 8052 Bible in another browser window!),"

One of the most frequent complaints about posters is that they haven't bothered to search for answers to their questions. If the exam encourages them to do so I'd say it can only be for the good. I also argued elsewhere in this thread that being able to locate answers is a valuable skill.

"I think a bigger concern is that someone besides the logged-in member could take the test for the logged-in member. Or they could share answers with others unless the pool of questions is so large that that isn't possible."

Only if you offer a cash prize for passing! The only thing they are going to gain from this is the ability to score others' posts and the satisfaction of having succeeded.

"And given the email I get about interpretations of karma scores, etc."

Precisely why I think the system should be scrapped or restricted to individuals who demonstrate that they are capable of making an informed vote.

"I just know someone is going to take the test, interpret a question differently and come up with an alternative answer, and then complain to me that their answer was right when they get 98% instead of 100% on the test."

Just give them pass or fail. Make the exam multiple choice so there can be no debate about which answer is the correct one. There's no need to reveal to the examinee which questions they got wrong. This should make it easy to automate (in the sense of calculating pass/fail from a bunch of check boxes), I know nothing about the mechanics of a web site).

"I'm open to more feedback on whether more people think an optional exam would be useful; but my first impression is that this may be one of those ideas that are good in theory but awfully hard to implement in practice."

I think it will make your life easier in the long run.