The proposed Google Book Settlement contains a significant number of assumptions concerning the motives of the participants.  One of the most obvious is that authors and publishers are in it, to put it crassly, for the money. 

That might not always be a good assumption.  Let's say the author of a book, in full possession of rights, wanted to include her book in Google Book Search, and make it freely available for use under a Creative Commons Attribution, NonCommercial, Share-Alike license.  The author might not feel the work is likely to generate much additional revenue, or regardless, wants her work to be broadly and widely accessible to the greatest number of readers possible. 

How would she do this under the settlement?  Is it possible?  Would she have to opt out?

The default assumption is that works would be fixed with a pre-determined (algorithmically derived) price:

(4.2)  Default Pricing Option.  If the Rightsholder of a Book has not specifically directed that its Book be sold at a Specified Price, then Consumer Purchase of that Book will be sold at the Settlement Controlled Price.

The immediately prior clause states that the author can specify their own price:

(4.2)  Specified Price. In this option, the Rightsholder identifies the price for which it wants its Book authorized for Consumer Purchase to be sold. This pricing option is referred to in this Settlement Agreement as the "Specified Price."  The Specified Price may only be changed by the Rightsholder and is not subject to Article IX (Dispute Resolution).

Does this mean that the author can set a price of "free" -- and more importantly, if they can -- is there any mechanism by which to convey the license (Creative Commons or other) under which that freedom of access is governed? 

One potential problem with this settlement is it's enforcement of a set of license and pricing assumptions that might be difficult to unbundle.  In this fashion, the settlement assumes the primary motivation is profit maximization, not distribution to the greatest number.