I'm with @FF2. Since I chose to keep my unlighted official Kindle cover, I found it caused problems with either an inadvertent page turn (pressure on the keys prior to sleep mode) or a freeze (the oft-reported grinch). A 5-second power switch hold will blank the screen. This apparently de-activates the Kindle enough that I have not had a cover problem in several weeks now, and re-awakening still takes the same 1-2 seconds as an automatic sleep mode power up. This is not the same as a total power off because it does not require the usual 45-second reboot.
I have trained my wife to do the same 'power down' when using her nylon protective case. I think it's a good idea to avoid trouble. During normal daily use, I let the self-sleep mode activate when I'm not using the cover which is most of the time.
