Version 3.7 will not make most Internet software work unless you are already on BlackBerry Enterprise Server.
There are a lot of people that have succeeded on BlackBerryOS. Some people have problems. Not everybody does. If you are not having problems with 4.0, do not bother downgrading, especially if you are on a BlackBerry Enterprise Server (wireless Outlook synchronization, Addressbook, Calendar, Contacts, etc, is a big feature of 4.0 if you are using BES/MDS)
I have made updates to this document:
http://www.blackberryforums.com/viewtopic.php?p=20472
This is required for North American carriers.
I don't have detailed information for Hong Kong carriers or other countries (Remember, I'm just an unpaid volunteer, this is a hobby.)
And singberry/PhilJJ, there are already
instructions about downgrading BlackBerryOS -- It's posted as a sticky in the General forum. Didn't you notice? ;)