CURDATE() returns the DATE part of the current time.
NOW() returns the date and time portions as a timestamp in various formats, depending on how it was requested
Example
mysql> SELECT NOW(),CURDATE(),CURTIME();
+———————+————+———–+
| NOW() | CURDATE() | CURTIME() |
+———————+————+———–+
| 2012-06-18 14:14:01 | 2012-06-18 | 14:14:01 |
+———————+————+———–+
1 row in set (0.03 sec)