Yahoo has announced that it will be offering an opt-out function for customized advertising to searchers by the end of the month.
The announcement comes as Yahoo has responded to a Congressional letter seeking information about data collecting and online advertising practices. You can read Yahoo's full response here.
Google has also responded to the letter with features expected to be rolled out in the future. One feature is ad capping, which allows advertisers to limit the number of times a user sees a targeted ad. Ad capping is a DoubleClick feature that Google will be integrating to their Content Network. They say this will benefit users, since they won't be seeing the same ad over and over again. You can read the full context of Google's response here (pdf).
Microsoft is still working on their response, and it will be largely based on Mike Hintze's testimony before congress last month.