Hypothetical: a Windows 7 or 8 computer has a self-encrypting hard drive. It is stolen with the power on, but with the Windows lockscreen on. Are there easy off-the-shelf ways to access the data on the drive? All of the password recovery mechanisms I see for Windows 7/8 appear to require a reboot, which would drop the decryption key from RAM. I'm not concerned with intelligence-agency stuff so much as what would be available to the average petty criminal.
It simply requires a entry level of electronics knowledge to do this. The average 'petty criminal' wouldn't care since they would simply sell the stolen hardware (also they most likely would not care in the slightest). Your danger would be if your average house-thief was effectively being sub-contracted by someone with a little bit more knowledge/experience and the intent to commit identity fraud or steal your data.
You RAM is going to need to be 'refreshed' every once in a while ( and by that I mean nano-seconds. ) when this occurs the ram is read and written to, and the pins are visible right there.
If DDR ram is cold/frozen then the data contained within a ram chip can actually survive not being refreshed for more than long enough for the ram chip to be removed, and dumped.
Once a full ram-dump occurs then ram can be replaced with a simulator and the machine can be instantly returned to its previous state with the ability to even disable the lock screen ( or alternatively just grab the HDD Decryption keys out.
There are also attacks which can be used to intercept data inline via attaching debuggers ( a lot of Nintendo 3DS / Wii / WiiU research used those techniques for sniffing live ram. )
Your best bet against the first attack I described would be to migrate to a machine which has its ram soldered directly onto its motherboard ( I know for a fact the macbook air does, as do the majority of video game consoles. )