I believe the reg key in question is already removed from most custom ROMs. So if it is not there, don't worry about it. I think (could be wrong) that that particular hack was more related to avoiding error 67 when tethering via ICS when you don't already have a data connection running.
I remember being worried about an outrageous bill when I first start tethering, which was years ago now. I've never once received a bill with extra data charges. Don't use it as your primary internet connection, but if you're not stupid about it I wouldn't worry. These days I probably use a couple of gigs a month streaming music/video in my car and around town.
PDANet will not work over WiFi, but you don't need PDANet, USBModem, or any other dial up modem software. They don't hide anything from anyone. I'm not sure why some people believe that they do. Maybe just a security blanket kind of thing. Use the built-in Internet Sharing for USB and BT tethering. WMWiFiRouter (which relies on Internet Sharing/ICS) is great for WiFi access.
Just remember, keep your data use reasonable (don't do
all your P2P traffic over it) and you'll be OK. Have fun!
