Something

mysql> select @counter := 0;
+---------------+
| @counter := 0 |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT Date, Status, IF(Status = "1", @counter := @counter + 1, @counter := @counter - 1) AS Counter FROM (
    ->   SELECT usageOtherTime as Date, "1" as Status
    ->     FROM KSUsage
    ->     WHERE
    ->       usageEvent = 16
    ->       AND usageOtherTime BETWEEN '2006-06-06 00:00:00' AND '2007-06-07 10:00:00'
    ->   UNION SELECT usageWhen as Date, "0" as Status
    ->     FROM KSUsage
    ->     WHERE
    ->       usageEvent = 16
    ->       AND usageOtherTime BETWEEN '2006-06-06 00:00:00' AND '2007-06-07 10:00:00'
    ->   ORDER BY Date
    -> ) AS Ordered LIMIT 50;
+---------------------+--------+---------+
| Date                | Status | Counter |
+---------------------+--------+---------+
| 2006-06-06 07:28:03 | 1      |       1 |
| 2006-06-06 07:32:42 | 0      |       0 |
| 2006-06-06 07:39:02 | 1      |       1 |
| 2006-06-06 07:46:59 | 1      |       2 |
| 2006-06-06 07:47:21 | 1      |       3 |
| 2006-06-06 07:53:27 | 1      |       4 |
| 2006-06-06 07:53:29 | 1      |       5 |
| 2006-06-06 07:54:05 | 1      |       6 |
| 2006-06-06 07:54:34 | 1      |       7 |
| 2006-06-06 07:57:25 | 1      |       8 |
| 2006-06-06 08:02:06 | 1      |       9 |
| 2006-06-06 08:02:24 | 1      |      10 |
| 2006-06-06 08:02:25 | 1      |      11 |
| 2006-06-06 08:02:30 | 1      |      12 |
| 2006-06-06 08:02:53 | 1      |      13 |
| 2006-06-06 08:03:05 | 1      |      14 |
| 2006-06-06 08:03:06 | 1      |      15 |
| 2006-06-06 08:03:09 | 1      |      16 |
| 2006-06-06 08:03:11 | 1      |      17 |
| 2006-06-06 08:03:20 | 1      |      18 |
| 2006-06-06 08:03:52 | 1      |      19 |
| 2006-06-06 08:04:12 | 1      |      20 |
| 2006-06-06 08:06:11 | 1      |      21 |
| 2006-06-06 08:06:49 | 1      |      22 |
| 2006-06-06 08:07:31 | 1      |      23 |
| 2006-06-06 08:14:39 | 1      |      24 |
| 2006-06-06 08:18:50 | 1      |      25 |
| 2006-06-06 08:19:53 | 0      |      24 |
| 2006-06-06 08:24:31 | 0      |      23 |
| 2006-06-06 08:24:46 | 1      |      24 |
| 2006-06-06 08:34:44 | 1      |      25 |
| 2006-06-06 08:34:44 | 0      |      24 |
| 2006-06-06 08:34:54 | 0      |      23 |
| 2006-06-06 08:35:45 | 0      |      22 |
| 2006-06-06 08:37:22 | 0      |      21 |
| 2006-06-06 08:37:30 | 0      |      20 |
| 2006-06-06 08:37:38 | 0      |      19 |
| 2006-06-06 08:37:47 | 0      |      18 |
| 2006-06-06 08:38:56 | 0      |      17 |
| 2006-06-06 08:40:46 | 1      |      18 |
| 2006-06-06 08:45:55 | 0      |      17 |
| 2006-06-06 08:46:14 | 0      |      16 |
| 2006-06-06 08:48:26 | 0      |      15 |
| 2006-06-06 08:48:26 | 1      |      16 |
| 2006-06-06 08:49:27 | 0      |      15 |
| 2006-06-06 08:52:15 | 0      |      14 |
| 2006-06-06 08:55:49 | 1      |      15 |
| 2006-06-06 08:57:18 | 0      |      14 |
| 2006-06-06 08:58:38 | 1      |      15 |
| 2006-06-06 09:06:51 | 1      |      16 |
+---------------------+--------+---------+
50 rows in set (8.36 sec)