Im no expert on isps nor wish to be and have to say i have stuck with bt since getting adsl. But when the service level has dropped they soon sorted out the problem and i made sure i got refunded for poor service. I understand where your coming from i can remeber the mobile phone companies messing people around if they wanted to quit, get a puk code or transfer a number but slowly it changed.
Hopefully the same will happen with the isps as customers wise up to who to avoid.
In the majority of our customers we do have control of their testicles due to our service contracts.
If they mess us round we have withdrawn/reduce our services software, hardware and/or techincal support and trust me that could bring a company to its knees very quickly.
But after a while we would have few customers as customers would move to other companies once their contracts were finished.