Warning for everyone else currently a happy AdWords customer: go through your lists, look for words which are under 1% CTR, and *scrub*.  My best performing keyword has, over the past month, 1.75% CTR.  It dipped for about a week below 1%.  Random fluctuations, you would think, but Google responded by quadrupling the cost of it.  And even if I pay that for weeks to rehabilitate the keyword there is no guarantee that the minimum bid will ever go down.