My particular bugbear is that a fielder can throw the stumps down and, provided the batsman isn't run out, he can then continue to run off the deflection. To me that's not fair - a fielder has done a smart bit of work, hit the stumps, and then gets penalised for it.
In that particular instance, the extra run isn't penalising that fielder, though; it's penalising the peanut(s) who wasn't/weren't backing up the throw.
For mine, the front-foot no-ball rule has to change. It's so hard to get it right and umpires routinely bugger it up and the umpires' attempting to get it right affects their ability to judge things once the ball has left the bowler's hand (i.e. LBW's and fine nicks). I see virtually no advantage being gained by a bowler being 1mm in front of the line vs 1mm behind it yet one results in a no-ball and the other does not and denies some bowlers wickets. And with really close ones, parallax errors mean umpires can sometimes err and no-ball a legitimate delivery which sometimes results in denied wickets.
So I say, sacrifice the front-foot rule, either revert to the back-foot rule or make the no-ball calls automatic and make umpires' jobs easier in adjudicating decisions at the really important end.