Quoting the relevant portion of this email:
http://lists.wikimedia.org/pipermail/wikitech-l/2010-October/049813.html

Right now, it takes a sharp eye to notice when one is looking at a
page that hasn't been accepted yet. The main visual indicators are an
icon on the right, and the fact that the "Pending Changes" rather than
the "Read" tab is highlighted. What we plan to do here will be
modeled on what you see when you're looking at an old revision (i.e.
there will be a horizontal notice at the top indicating "This is an
pending revision of this page, as edited by 127.0.0.1 (talk |
contribs) at 13:37, 7 October 2010. It may differ significantly from
the accepted revision.")

An old decision that we plan to revisit: currently, the revision you
are shown depends on whether you're logged in or not you are logged
in. If you're not logged in, then by default, you see the accepted
revision. If you are logged in, you see the pending revision by
default. Brandon feels pretty strongly that we need to be much more
consistant here, always showing the accepted revision regardless of
logged-in status. There's some research we need to do to make sure we
understand the current rationale, but barring any unexpected insight,
we'll probably be making the switch.

Brandon proposes a design here:
http://www.mediawiki.org/wiki/Pending_Changes_enwiki_trial/NovemberReleaseDesignChanges

I believe this one was addressed by r76835