The web world is abuzz with the announcement from TW Cable that they will begin adding charges for the bandwidth hogs (TechDirt and ISEN). About 5% of the users disrupt the network for the rest of the 95%. Comcast tried traffic shaping, but the FCC is all over them. (See Rulemaking WC 07-52). DOCSIS is as asymmetric as ADSL -- more download than up. That's why P2P upsets the apple cart.
This will get funky now that TV over the Internet is booming - Apple TV, Amazon, Netflix, Hulu, Joost. (This is mainly a Residential ISP issue. So if you are a B2B ISP, go back to counting your money).
The problem is that not only doesn't Grandma know what the limit is or when you would be over --- I don't either. My EVDO card is a backup, so I only have the 40MB for $40 deal. Sometimes my email is 20MB while at a conference (mainly Cliff's fault). Sometimes it is less than 4MB. Web page size has grown to an average of 1.4MB (I read that somewhere). We'll see how all this plays out, but the genie is definitely out of the bottle. The days of oversubscription and mainly bursty internet traffic are narrowing due to video.
Updated thoughts: Will the cap increase with the Tier I buy or id the cap the same if I buy 7MB or 15MB? Again, how will be measure usage? Will the cap be fixed and named or arbitrary (like 10% greater than your metro average)?