I always presume that we know more than they do. But knowing how much they're cracking down on this, I wouldn't put it past the company to come up with some flawed method of detecting connections.
I have always used tons of data ever since I got my Inspire in March 2011 (as well as a warranty replacement I got in June 2011) and I never got anything about tethering from them before this week. I never even got a throttle txt msg until two months ago (even though I kept going over and around the end of last year I hit 10GB and was never notified or throttled). The rep I saw in the store and the rep I talked to on the phone this week both told me that just because I am an extra high data user, that alone would not trigger the anti-tethering messages (which is the way it should be but who knows what they're actually doing in reality).
Everything else so far isn't a big deal aside from the common sense things like Pandora and Google Music which not only use their own amounts of data but also use the identical extra amount of data as "Streaming Media" (in other words if I use 55 MB of Pandora, it also uses 55 MB of Streaming Media, which seems like double-dipping to me). I also didn't realize that I am averaging about 10 MB per day in web surfing and 5-7 MB per day in Gmail and almost 100 MB per day on Instagram (yikes! that is stopping soon for sure).
But anyway, getting back towards the original point, if they're simply saying that someone is tethering just because of high amounts of data being used, that's really not fair considering the things that can't be stopped on some phones. I mean, we buy these phones which have bloatware to begin with and the bloatware uses data without our knowledge, plus that behind-the-scenes data use for DCS Service. That alone could turn out to be 1800 MB this month for my phone even though the only auto-sync items I have selected are the built-in weather updates and Gmail and Calendar and Contacts (I don't use any of the others). So I can't even begin to imagine how much data I would use if I did indeed try to tether.