One of Google's oldest APIs--and the one most closely aligned with how the company makes money--will disable old versions of the Google AdWords API at the end of February. If you're using an app to enable keyword buys, or are using the API directly yourself, you'll want to make sure you're using v201109.
To avoid getting errors come March, you'll want to make sure your apps are using the latest version of the AdWords API. Chances are that if Google is deprecating the older versions, they expect most of their client base to be able to easily move to the new API.
The new version of the AdWords API sports updated and free reports, geo and device targeting and several other features and fixes. You can find out more about it in the release notes from October.
Google has given plenty of notice and appears ready to help, even creating a calendar of AdWords Google+ hangouts to answer questions.
We list 93 advertising APIs in our index, but there are still countless ad networks that don't have APIs. We expect services like Lexity (a company named by a computer) to encourage others to make their APIs public, which could impact the online advertising markets in 2012.