The development team of Windows 7 in its blog posted an interesting post , which tells about the problem of the spread of malware by automatic launch (autorun) from removable media. Below is a picture of the dynamics of infections in this way.
To ensure security, in Windows 7, a similar mechanism that allows malicious code to be easily distributed will be disabled for all removable media. At the same time, the autoplay mechanism and all its components will remain unchanged. It is also reported that all this does not affect the optical disks with which autoplay / autorun will work in the old manner.
update: it is also reported that this restriction will also be introduced in XP / Vista