mysql slave trailing behind

[Mikael Fridh]

One of My MySQL slaves is trailing behind its master.

| 42 | system user |           | NULL | Connect | 8193 | Has read all relay 
log; waiting for the I/O slave thread to update it | NULL             |

8193 seconds behind.

Why might the slave be trailing?

I just did a
slave stop;
slave start; 
and the slave is catching up really fast again!

We have 4 slaves reading from that master.
Is it a problem on the master or on the slave?
(too many slaves reading from it?)


(while writing this the slave has caught up to 1200 seconds behind.)

Mike