I have found that using sleep/suspend mode on the M17x has been problematic at best. Most of the time when waking the unit up, I am greeted with a blank LCD and no way to work around it short of a hard reset (holding down the power button). I have observed this behavior with 179.85, 186.12 and the 186.24 drivers. I know from past experience this is almost always a display driver issue.
There is currently no work around to this that I can find. I have tried disabling the 9400M G (motherboard GPU) prior to putting the system to sleep (via the FN+F7 command) has met with poor results. Sometimes it will work and wake properly, other times it will not.
I will be testing the current line of drivers (190.xx) series this weekend. I plan to disable the mGPU (via the BIOS) and install the 190.40 driver from xfastest.com and see how it fairs. If sleep is still an issue, then I'm going to label this as a severe problem. If the unit enters and exits sleep mode without issue then it will confirm its poor driver implementation.
Bottom line, my opinion is this: A laptop is used for portability. If you cannot put the unit to sleep and transfer it to another location (i.e. conference room to office, etc.), then what is the point in having a laptop? One of the selling points to the M17x is the integrated GPU (mGPU). The mGPU provides greatly enhanced battery time but at what cost? A non-functioning sleep mode? Not acceptable in my book.
I can only hope that Alienware/Dell resolve this issue soon. If this is truly the 'All Powerful' laptop, it should function properly out of the box without having to cripple certain features. Most would agree.
More to follow on this 'bug'.