Some time ago, I added a Crucial m4 256GB SSD to my iMac. The performance boost was even better than I expected - the iMac now writes data about 2.5 times faster than the stock hard drive, and it reads data over 5 times faster - considering how much time I spend working in front of a computer, this really improved my day! What didn't improve my day, however, was that some time ago, I noticed that my iMac would never wake back up after it went to sleep; I might get as much as the login screen to appear, but the time would be wrong and the password prompt either wouldn't appear or wouldn't function. I feared the worst - that the SSD or the original hard drive were failing. I tried changing the power saving settings, disabled powering down the hard drives when they weren't in use, etc., but the problem kept occurring. Even if I prevented the computer from sleeping using the free utility Caffeine, it would still lock up at some point.
I was about to disassemble the iMac to replace the SSD (which is no simple task - it requires using suction cups to remove the screen, disconnecting the entire LCD and disassembling basically the entire computer) - that's when I decided to try Google'ing for the problem one last time. Yet again, I couldn't find anyone with the same symptoms as my iMac - specifically, beach balling on the wake/login/lock screen after the computer has gone to sleep. But I kept searching, and stumbled across a notice from Crucial about a firmware update for my SSD, which included a note about resolving issues when the hard drive is powered back up after being spun down or put to sleep. I didn't think it would apply - after all, I had changed the System Preferences to disable ever powering down the hard drives, so that shouldn't be possible. I decided to give the firmware update a try, though, since it would save me from having to disassemble my iMac!
Crucial doesn't have a firmware updater for the Mac, so I downloaded the "Manual Boot File" firmware update package from the Crucial m4 firmware update site. I burned it to a DVD, and then rebooted my iMac, holding down the Option key on the keyboard to force it to allow me to select what drive or disc to boot from. The Crucial firmware updater appeared as a CD labeled 'Windows'. I selected that, selected yes to allow the updater to continue, and then crossed my fingers. Once the firmware update completed, I rebooted my iMac, and much to my surprise, the firmware update completely resolved my issue!
So, if you have an iMac that you've installed a Crucial m4 SSD in - update the firmware! And don't assume that the problem isn't related to powering the hard drive down or putting the hard drive to sleep, because apparently even if you unselect this option from the Energy Saver preferences in System Preferences, OS X is still trying to put your SSD into a lower power mode.