I don't know if this has been done but I think it's quite useful:

http://www.okcupid.com/tests/take?te...00288064322170

What did people get?


My result:

Native language: English
Score: Advanced
You scored 92% Beginner, 100% Intermediate, 86% Advanced, and 73% Expert!
'You have an extremely good understanding of beginner, intermediate, and advanced level commonly confused English words, getting at least 75% of each of these three levels' questions correct. This is an exceptional score. Remember, these are commonly confused English words, which means most people don't use them properly. You got an extremely respectable score'.

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It can be hard for native English speakers, but it shows the common mistakes that native English speakers make, so if you learn and get these right, you know you're doing well.

So obviously if you get a low mark it's still more of an achievement than what it says.