I live in Scotland, and I recently signed up with an ISP that did this. They have block control over my building, so there wasn't any other solution. They have a device (I'm pretty sure it's just a linux box based on my nmapping) that looks at each packet's TTL. If the TTL is odd and the port is NOT 80 or 443, it drops the packet. If the TTL if odd and the port is 80 or 443, then it redirects you to a billing page.
I bypassed it by incrementing TTL at my gateway. I imagine people will modify openwrt/dd-wrt to do this as well. Additionally, I have a solution which tunnels my connection over a VPN to an Amazon EC2 instance and does some magic to beat QoS. It seems like oversubscribing at at least 2000% seems typical. I'm paying for a 50 mbit/sec connection. I see closer to ~6-8 mbit/sec (no, I'm not getting my megabytes and bits confused). Additionally, since I know a little about my ISP internally, they run all these blocks to their HQ over MetroE-like products, and then concentrate it into their core. Their transit is 10GigE (based on traffic numbers pulled from various private sources). I know that they sell far more than 10GigE of bandwidth to customers. There is far more wrong with the ISP environment here than you'd know.
My girlfriend's ISP is even worse. They do a significant amount of throttling on specific ports (1935, 80, so on..) and basically any kind of download during the day slows down to a halt. They have about 6000 people + several offices on a 10 GigE connection.
I don't know if this will even be seen, but I thought it was worth throwing out there.