I was doing the dreaded master merge, facing merge hell, and feeling kinda glum. But I found this as a way of breaking the problem up and merging only a manageable chunk at a time - say merge master as of 5 days ago:
$ git merge "master@{5 days ago}"
or master as it was 3 commits ago:
$ git merge master^^^
More work, sure, you have to potentially re-visit files, but it helps triangulate the hard spots. Indeed, you can do a backwards binary search for a manageable chunk.
More revision-vocabulary here: http://git-scm.com/docs/gitrevisions.html