"We're aware that some PS3 users are reporting issues after downloading and installing the 2.40 firmware update onto their system," said a rep.
"We are looking into the matter further and will work with our customers to address any related issues they may be experiencing with their PS3 systems."
On the official Sony PlayStation boards, there is currently a 42 page thread based on the problem, and I would implore current PS3 users to check it before deciding to update to 2.40.
View that thread here: PS3 official boards.
Update: It appears that Sony has taken the firmware update down as many users are confirming they can no longer update through the console or download from the Sony site.
"We have temporarily taken firmware v2.40 offline," said Sony Computer Entertainment America corporate communications director Patrick Seybold. "We've received a limited number of calls from consumers experiencing an issue with installing the system software update on their PS3. While our consumer services department has seen a low volume of calls on this topic, we are committed to providing the PS3 community with XMB access features delivered in the v2.40 update. We are working diligently to isolate the problem for those few consumers and to identify a solution before we put the firmware back up."