Practical advice: Avoid allowing your computer to go into sleep mode if possible. Your data may have a greater chance of survival if you shutdown properly. Do not assume sleep and awake technology will work properly every time.
If you are going to step away from your computer for a while, it is better to shut it off. As inconvenient as it may be, closing down can be the right decision. Exit all programs, save files, wait a minute to be relatively confident the system caught up with the file saves and exits. Shut off the computer.
That is one of the basic insights I garnered after a week exploring the results of deep sleep modes in an operating system I was using. After some more exploration on the Web, I now think it is good advice for other large operating systems as well. It only takes one badly exercised power resume moment to wreak havoc on data. Sleep and resume technology remains a work in progress. Wake and resume should not be assumed as reliable until significant progress has been made in the development of the technology.
You can read more about the experience that produced the insight in the article, Vigilance Regarding Data Corruption in Linux. It explains a general observation about data corruption following wake and resume. As reports on the Web seem to indicate, it is an issue experienced across mainstream technologies.
Wake and Resume Problems Around the Block
The following is a short list of wake and resume problems available from a web search. Contrary to my initial assumptions, the problem of wake and resume is more common than I thought. Long-term it may be better to migrate away from the sleep mode concept altogether and embrace alternative approaches.
Ubuntu and Sleep/Resume
Microsoft Windows and Sleep/Resume
Apple and Sleep/Resume
BSD and Sleep/Resume
Wake and Resume Issue Needs Work
I was never interested in ACPI technology. Sleep mode technology does not resonate with me as I view it as a less optimal way to address the concerns for which it was designed. Never explored why. All I will say is that dumping memory to a file and replaying it all back accurately, all the programs, activities, executing code, etc, just did not seem as if it could be done reliably every time. Of course there are risks in booting systems, but that process seems much better understood. The sleep, wake and resume functionality works more often than it fails though. Despite that, a bit of preparation may help head off certain kinds of data impairment.