I just installed it and someone was saying that some guys are having their ps3 bricked because of this update. A quick check at PSN singapore reveals the following:
Urgent notice about PS3™ system software ver. 2.40
03/07/2008
We have been reported from a limited number of PLAYSTATION®3 (PS3™) users that XMB™(XrossMediaBar) is not displayed after updating to the PS3™ system software ver. 2.40. We have temporarily taken system software ver. 2.40 off line and are currently conducting investigations to determine the cause of this problem. We will announce through our website as soon as we are ready to resume the system software update.
We apologize for the inconvenience and appreciate for your understanding.
Great... just great.
Hopefully nothing happens to my beloved ps3 in the meantime.