There's two problems:
1. The device crashes (becomes unresponsive, won't turn itself off) when waking from sleep.
A few people reported this problem prior to the 20111117 update. Since the update, a lot more people are seeing this problem (including me).
Fortunately, there's a
workaround: set the "WiFi sleep mode" to "never."
Probably a very high priority for the Kobo Vox development team!
2. Why is the device waking up from sleep every few minutes in the first place? Apparently this is caused by one of the pre-installed applications, doing some kind of periodic check.
I'm guessing this is probably not such a high priority.