We plan to add a Default Date/Time serialization/deserialization in version 
1.2.  The
tricky thing about this feature is that we do not know the format that the 
client
supports.  If the system using the GSON library passes these JSON serialized 
object
back and forth and serializing/deserializing on both ends then its a non-issue 
for
which format is supported; however, if you used the serialized version for 
display
purposes then the date format matters.

For the time being, you can register the following Type Adapter:

/**
 * A default type adapter for a {@link Date} object.
 *
 * @author Joel Leitch
 */
public class DateTypeAdapter implements JsonSerializer<Date>, 
JsonDeserializer<Date> {

  private final DateFormat format = DateFormat.getInstance();

  public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext
context) {
    String dateFormatAsString = format.format(src);
    return new JsonPrimitive(dateFormatAsString);
  }

  public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext
context)
      throws JsonParseException {
    if (!(json instanceof JsonPrimitive)) {
      throw new JsonParseException("The date should be a string value");
    }

    try {
      return format.parse(json.getAsString());
    } catch (ParseException e) {
      throw new JsonParseException(e);
    }
  }
}


// Create a GSON instance that can serialize/deserialize "java.util.Date" 
objects
Gson gson = new GsonBuilder()
    .registerTypeAdapter(new DateTypeAdapter())
    .create();

Submitted the type adapter to support this feature (r130).  Still need to 
update the
GsonBuilder class to make the Date TypeAdapter configurable without requiring 
the
adapter to be registered.

The change r145 contains the last piece of code required to close off this bug. 
Removed the DateTypeAdapter from the public API so that it can only be 
configured via
the GsonBuilder.