Your files are only really safe using programs like TrueCrypt or PGP while the encrypted file is not "mounted." There are ways to get the password when the system is "live." Example legit hacking program here --
http://www.net-security.org/secworld.php?id=9077 . However, we're still safe while our files are not mounted.
When is this a high risk? When you use sleep mode rather than fully powering off.
Also if someone has access to your physical computer you might as well bend over now (for example, installing a keyboard logger or just a hidden camera looking over your shoulder).