I have posted an update of my Minnesota recount scorecard here.

As many have remarked, the rate of challenging has certainly picked up.  I have been expressing challenged ballots as a percentage of residual votes in the Senate race, since the challenges probably showed up originally as over- or under-votes.  Overall, 14% of residual votes have ended up in the challenge pile.  Among ballots counted today and over the weekend, 38% of residual votes have been challenged.  The campaigns are obviously going for broke, hoping to catch some slack from the state board, when it gets to that stage.