I also received the 4.00.01 update today. I know I don't have to bother to call the LG Service because the Dutch and Belgium ones are one and the same. I'm very curious to what they've changed in this update. I walked through the menus but i couldn't find anything.
I just contacted LG through their @LG_WEBCARE_NL twitter account and they had some info:
"Algehele optimalisatie en stabilisatie in de werking van functies. Dat zul je automatisch merken op jouw toestel" in English: "Overall optimalisation and stabilisation of the features wich you will notice when using your unit".
So... I don't know if they didn't know better at the twitter service desk or the update wasn't really that big. (3.xx to 4.00.01 sounds big to me)
I have a 42LD650 and my firmware also got updated. Since then, my USB disk disconnects in the middle of the movies, streaming from DLNA server interrupts and TV switches to Antenna input... Waiting for a way to downgrade the firmware.
And i would like to know the details about improved stuff in that upgrade.