I use "wheezy" latest release. The device provides some web service features and supposes to be active 24/7. However if the server wasn't requested for certain amount of time (it is hard to tell exact time), the device seems going to sleep (hopefully not crash). The device connected to net using wi-fi dongle. I found some answers here that a reason of device freezing can be that wi-fi card is going in economy mode, so I followed the instructions and can confirm that the dongle doesn't go in sleep but it starts blinking like getting not attended from computer. it means that device still goes in sleep although wi-fi is awake. The solution as buy another raspberry pi and make it all time pinging sleeping one doesn't work since only being a server getting requests prevent device going to sleep. Trying to poll something from the device doesn't prevent going in sleep mode. I can't actually confirm that device going to sleep. I do not have monitor or keyboard attached, and attempt to attach something issues rebooting of the device. So I am currently out of clues what can issue the behavior. And yes, I applied all remedies preventing OS crashes as no turbo and increased minimal VM memory size.