In yesterday's Google AdWords blog entry named Yesterday’s release has been rolled-back says;
We have identified a bug in yesterday’s release and are working to correct the issue. In the meantime we have rolled-back the latest release so your future operations will not be affected. Once the bug is fixed we will notify you and re-release the code. We apologize for any inconvenience this may have caused.
But supposedly it was a major issue for those customers who used the API daily (big customers). One advertiser wrote to me stating, "Their new API release erased all the destination URL’s. This had a huge impact on a number of SEM firms including us." The Google Groups AdWords API Forum has more details.
There is also a forum discussion taking place at SEW Forums. In that discussion the thread creator has a good explanation of the issue;
Basically anybody (themselves or their bid management service) using the API to manage their bids will be affected by this problem. What happens is that when any bid was changed for a keyword using the API, that keyword’s “destination URL” would get deleted and would change to that ad groups default URL. This is happening each time a bid was changed for every keyword.
AussieWebmaster clarifies that "this was not limited to bid interfaces. The Google internal tools for mass uploads were also effected as they use the API."
Good thing for versioning systems, at least they were able to roll back to a pervious production release.