Note: Steve was exaggerating a bit, or this post misrepresents what he said. I can think of 12 just off the top of my head.

That said, many of them fit the same pattern:

    reddit_thing_link
    reddit_thing_comment
    reddit_thing_user

...and each had a complement with "data" in place of "thing".

Though there were also ones like:

    reddit_xref_subscription_user_subreddit
    reddit_xref_vote_user_link
    reddit_xref_vote_user_comment

...for the many-to-many relations.

That accounts for most of the big ones (though there are also a handful of smaller specialty tables, too.)

Also, the above is as of March 2011 -- a lot has moved to Cassandra since then.