Got my first Captivate on 9/20, even stock after a full charge and taken off the USB cable, it would not wake up after a few minutes...every time. Battery drained down to 92% or less it would quit doing it. Full recharge, same issue when pulled off the charging cable. Swapped it out 9/27, second Captiviate was actually a lower serial number than previous unit, battery date was the same, and I assume from the same batch. Same issue as the first...everytime I removed it from full charge it would not wake up from sleeping after a few minutes of being locked.
Updated to Cognition w/Froyo and not a single shut down since. Been a couple weeks now.