I’ve been following the Ars coverage of the Oracle v Google trial regarding whether Google’s use of Java APIs is “fair use”. I didn’t think Google would win, but was pleasantly surprised when the jury decided in their favor. Hurrah!
However, just because Google won, doesn’t mean that companies can indiscriminately copy APIs and have it fall within “fair use”. It seems safest to me to make use of APIs that fall under an open source license. That way, the code individuals and companies write can more easily be run against competitive API implementations without being held hostage by the owners of the original API.