EntityFieldQuery select entity if at least one tid is in the array? This seems like it would be a common need but I don't see how it can be done with the operators available. I have a taxonomy reference field that allows multiple values. I would like to construct an EntityFieldQuery that selects the entity if at least one of the tid's is in the given array.

$query-&gt;fieldCondition('field_tags', 'tid', $tid_array, 'CONTAINS_ONE');
All you need is:

$query-&gt;fieldCondition('field_tags', 'tid', $tid_array);

From EntityFieldQuery::addFieldCondition():
"The operator can be omitted, and will default to 'IN' if the value is an array, or to '=' otherwise."