On the 15th March 2011 Google will be changing the way you bid on the display network in order to simplify the system.
Currently there are three different default bid settings for managed placements: a regular default bid, a managed placements bid, and a display network bid, which can be a bit confusing and rather inept if you choose to set individual bids for managed placements.
Therefore in mid-March Google will be removing the managed placements max. CPC bid, so you will be able to manage both the default bids for both automatic and managed placement bids by setting just the Display Network default bid. Individual bids will also be set for managed placements in the same as they are currently.
Google has sent out an email announcing the change and the steps they have taken to ensure that the change has no impact on users current bid amounts or where they currently appear, explaining how the changes will affect your account:
Any managed placements with individual bids will still keep those bids, so if you choose to set your management placement bids individually then these changes shouldn’t make any difference to your ads.