Hi,
for those of you who also miss the seeing base revision in merge conflict markers sometimes, I recently saw this post on mercurial-devel:
http://comments.gmane.org/gmane.comp.version-control.mercurial.devel/45022
There is a reason why it is not the default behavior: mercurial collapses conflict regions when local and other have changed a few lines identically; this is not possible with 3-way markers.
Georg