As a follow up to the series of posts I've been making, I wanted to post what I ended up with.  Thanks to everyone who posted comments, your help was extremely useful. To recap, I have a working pair of events to add and remove partitions to this table:

create table log (
    logged datetime not null,
    id int not null auto_increment,
    text varchar(256),
    PRIMARY KEY ( logged, id )
)
PARTITION BY RANGE( TO_DAYS( logged ) ) (
    PARTITION p20080206 VALUES LESS THAN (733444),
    PARTITION p20080207 VALUES LESS THAN (733445),
    PARTITION p20080208 VALUES LESS THAN (733446)

I created my Events to handle adding new partitions (and removing old ones) from my log table and they seem to be working.  However, today I noticed that the events ran a few hours later than they ran yesterday.  

          EVENT_TYPE: RECURRING
          EXECUTE_AT: NULL
      INTERVAL_VALUE: 1
      INTERVAL_FIELD: DAY
            SQL_MODE: 
              STARTS: 2008-02-13 05:36:21
                ENDS: NULL
              STATUS: ENABLED
       ON_COMPLETION: NOT PRESERVE
             CREATED: 2008-02-13 05:36:21
        LAST_ALTERED: 2008-02-13 05:36:21
       LAST_EXECUTED: 2008-02-14 07:32:22

Thanks all for the help on getting my log_addpartition event running, dynamic SQL was just the ticket. 

I want to create a log table in 5.1 that is partitioned by day.  I want to roll-off old data and create new partitions for each day automatically.  Without writing a script and a cronjob, it seems like this should be possible with Events.  Let's start with the table:

create table log (
    logged datetime not null,
    id int not null auto_increment,
    text varchar(256),
    PRIMARY KEY ( logged, id )
)
PARTITION BY RANGE( TO_DAYS( logged ) ) (
    PARTITION p20080206 VALUES LESS THAN (733444),
    PARTITION p20080207 VALUES LESS THAN (733445),
    PARTITION p20080208 VALUES LESS THAN (733446)
);

This seems pretty straight-forward:  I take my log entry time and convert it TO_DAYS and partition on that.  I have tomorrow's partition all ready to go, just in case I don't get around to adding it today.  Let's create an Event to do add tomorrow's partition for us automatically each day: