I'm not sure if this site's admin has done or attempted this, but is there a way to add functionality to let users rate the difficulty of a question? This will give a good sense of what level of problem you missed on and even allow one to search for problems based on difficulty. Just a thought. Thanks!

Thank you for the suggestion - I will move it to the Suggestions thread shortly. You can "kind of" do it today already if you setup a poll - you can request users to rate the question - for example - I will set this one up as a poll. Is this what you meant? If not, can you please specify - I am interested to hear more.

Clearly, it would be great to have the ability to rate questions (created by default, not user arranged) and search them according to their difficulty. But, I guess there might be practical issues to have such luxury.

Thanks for the feedback - there is a thought in the back of my mind to possibly create a tagging system at GMAT Club - that would allow to tag easy/medium/hard/very hard questions and properly distinguish them but we are still ways away.