There is one big reason to get this firmware update - the drive has a built in 'fail' after 5000+ hours. Yes, you read that right... after so many hours, every 30 minutes to an hour, your Crucial M4/etc SSD will simply stop working because it thinks it has run too long.
I got back from a trip, and BSOD after booting and putting in a movie. WTF. Restarted and checked logs; did a quick scan; nothing. Restarted the movie and BSOD again. Shit. (right?)
Google search and found a post at Overclock.net which has copy/pasted text from Crucial's website which recommends the firmware update for my issue (which has since been removed).
Couldn't get the Win7 firmware updater to work, but burning the ISO image and running that worked fine. My SSD no longer fails every 30 minutes.
What a friggin ridiculous issue. A software 'fail' based on clock value... Crucial needs some new programmers.