@PlentyOfParsnips - no, I do not have a commercial interest in this at all.
@BaroqueAroundTheClock - there was never a suggestion that an ISP filter could, or should, provide the ability to give the control you are asking for.
However, that does not mean that they do not have a place. What I personally would like an ISP filter to be is:
Voluntary system that I have complete control over, with no government influence or control now or in the future. Therefore, no use for censorship (beyond stuff like the web-based child sex abuse that exists currently)
Adjustable so that I can logon to my personal ISP account and free / block specific URLs / domains as I choose.
Sensible applying the best practice of stuff like K9, Safeeyes etc, but allowing me to do this for the whole house in one go.
Knowing / Learning the difference between pornography and sites like Wikipedia / Mumsnet etc. The fact that MN has several references to anal sex should not cause the domain to be blocked by any sensible system, and I think suggestions that it would automatically cause problems are unfounded. Does it with PC based stuff?
Timed preferably allowing account holder to set it to automatically turn off at a personally set 'watershed' time if desired.
Easy to use having simple, click-button methods to add new sites, simple ways of unblocking desired sites etc.
Again, as said before, for many this could be a useful tool to help provide a first line of defence for a whole household. My experience with PC filters is that they too can be quite frustration, block the wrong stuff, be imperfect and slow down systems.
I accept all the statements about individual PC control, and this would not negate that if you wanted it.
I also grant that NetworkGuy comments re routers makes a lot of sense too, as quoted in PlentyOfParsnips thread. However, I still believe that the ISP filter has a place and part to play as a tool in all this.