Reading the history of the thread, it seems that OSL is either category B or category X. The only issue being:
"If You distribute or communicate copies of the Original Work or a Derivative Work, You must make a reasonable effort under the circumstances to obtain the express assent of recipients to the terms of this License. "
The same thing applies to AFL 3.0, which we've added to our category A list already (we can relicense AFL under AL 2.0, as long as AL 2.0 doesn't contradict AFL 3.0).
So the question becomes: "Is not being prepared to set up a click through website a reasonable circumstance?"
We make he reasonable effort of including the license terms in the download, but the circumstance is our own dislike for enforcing a clickthrough licensing policy on all of our mirrors (and our own servers). Given that we've been doing that for years, I do think that that is reasonable. It would not be reasonable to change our policies and technologies to fulfill this clause.
Any +1s for this being on category B?