I have a W520 and I suffered from this problem for a couple of months before solving it. I'm posting back here with the details in the hopes that it will help some of you, and also in the hopes that someone other poor soul might find this via a google search. It's an infuriating problem, though in the end it was probably my fault. I'm sure that this won't fix everyone's problems (certainly not the Linux people), but it has 100% corrected the problem for me.
My system is a Windows 7 Professional 64-bit, 16GB RAM, a Crucial C300 64GB SSD (internal) and a 500GB 7200 rpm drive (that came with the machine) (ultrabay). I'm not convinced that the SSD triggered the problem, but I do think it's noteworthy that I did a clean install of Windows 7 when I put in the SSD as my boot drive, and I did not install all of the Lenovo drivers. (I typically download everything but sometimes avoid installing drivers for devices that appear okay in Device Manager after the default windows install).
My symptoms were that sometimes (but not always) my system would not resume after sleep. I would see the keyboard light (above the display) flash on and the hard disk light would briefly flutter, but then it would sit there with a blank screen (not backlit), appearing to do almost nothing. Thinkpad buttons seemed to work (the mute button toggled the light on & off), but others did not (caps lock button did not toggle the light). If I left the system in that state for long enough (typically 15 minutes or more), it would eventually reboot, and I would get notified that a bluescreen had happened after the reboot completed (though I never saw the "blue screen" itself since the display was off). The BlueScreen error was a DRIVER_POWER_STATE_FAILURE (0x0000009f) in ntoskrnl.exe. And again, it typically didn't result in a bluescreen report b/c I almost always forced a reboot after realizing it was not resuming from sleep (usually within a minute or so).
While googling around for a solution to laptop bluescreens during resume, I stumbled across a post where someone asked about the driver used for the SATA controller, and did the person have an Intel SATA controller. I looked in Device Manager and found that I was using the default Microsoft SATA driver, although the W520 has an Intel SATA controller. I went to the Lenovo support site and downloaded the latest driver (http://support.lenovo.com/en_US/detail.page?LegacyDocID=MIGR-74430), and after installing it I suspended/resumed dozens of times with no recurrence of the issue. In fact, I don't think I've shutdown or rebooted since fixing this issue a couple of weeks ago. (After running the driver install program, you need to go to device manager, right click on the SATA Controller, choose Update Driver Software and the point to the directory where the driver software was installed by the exe you downloaded.)
It's interesting to note that the driver I installed is quite new (or was at the time of this writing), released on March 5, 2012. Also interesting is that the release notes list the following change: "(Fix) Fixed an issue where the computer might hang with 0x9F blue screen." I can't say with certainty whether the older Intel driver had the same issue as the Microsoft driver I was using, but I can say with certainty that *my* problem was fixed by installing only this driver (no other changes). So if you have the same symptoms I describe above, I think it's worth your while to try this fix.
Good luck!
