It all depends on how they accomplish it so I guess we will find out soon enough. I personally think they should only throttle people with high data for the month only when the towers they are on are very busy, then relax it when the towers are not.
I myself use WiFi for all my major streaming and I have a 16gig SD-card in my phone so I can keep a lot of music in my phone with no need to stream it from the cloud. It is mainly video and streaming music that burns up the data. Things like email is usually fairly low on use. Unfortunately FK23's data counter doesn't differentiate between Wifi and 3g/4g, but I can estimate that. I know that for the month (well most of it 11-25 to 12-22) I have used 1.74gig which would all be 3g/4g if I didn't WiFi most of it. There are also things you can do to lower your data use (do you really need your email app checking for mail every 15 minutes?). Also if rooted you can use Droidwall to to restrict on a per app bases what apps can use 3g/4g or WiFi you can limit them to only WiFi etc.
Codegerm