I have some trouble with an iPad 3G with OS 4.2.
Every time I put it in sleep mode, or if the iPad autolocks and it sleeps for more than 60 seconds or so, I am unable to wake it up using the Sleep/Wakeup button. The only way I can wake it up is by doing a reboot (home+sleep).
This only happens when the iPad is not connected to a power supply, if it is connected everything works.
This makes me suspect that something goes awry when it goes into "deep sleep" to save power and dumps RAM to disk... or alternatively when it restores RAM from disk.
I have tried restoring the device through iTunes but that didn't fix the issues.
Has anyone had a similar issue? Do you have any idea on how to fix it? The iPad was bought abroad, so I think my warranty options are limited.