Sites here and there seem to confirm that this closes the USB vulnerability:
http://exophase.com/ps3/ps3-firmware-3-42-hits-network-update-18063.htm
http://exophase.com/ps3/ps3-firmware-3-42-hits-network-update-18063.htm
Update: We can confirm that all variants of the USB-hub emulating exploit (PSFreedom, PSGroove, PSJailbreak) are no longer functional in firmware 3.42.