To answer your question - as far as I know, not as of yet.
But: Q2A was developed against a test database of 400,000+ posts (questions/answers/comments) and 100,000+ users, with a highly skewed distribution (i.e. some extremely active users, some inactive). Every single database query was designed and tested so that it runs very quickly against a large database, i.e. that it has the appropriate indexes available.
Since every page view runs efficiently, Q2A should have no problem with huge traffic and hits. Obviously it depends on the server, but I would say that the majority of page views should take under 0.1 seconds in total (CPU+disk+DB). That means it has capacity for at least 400,000 page views per day on one server, taking into account the fact that traffic isn't spread out evenly during each 24 hour period. (My rule of thumb: peak traffic is about double average traffic.)
You should be able to increase this much further by following the steps here:
http://www.question2answer.org/advanced.php#fast
And if you ever discover that a particular page view is taking consistently longer, it should be easy to solve the problem. It will likely just require providing a hint to MySQL to use a particular index for that query.
