Why not have the sites taken offline?
Funny thing. You never hear a word about actually removing the sites in question. Here in Germany, a private organisation chose 20 sites from the Danish blocklist and notified the respective hosting services. Within one day, 16 of those sites were offline and 3 more were checked but found to be legal under local laws. (Comment in German citing this experiment: http://www.heise.de/ct/Die-Argumente-fuer-Kinderporno-Sperren-laufen-ins-Leere--/artikel/135867)
The BKA always complains this is impossible or not feasible. A site that recently made fun of the minister of interior and his terrorists-are-everywhere campaign got taken offline by one call from the ministry to the hoster. However this is deemed to be infeasible for a child-porn website even if it is hosted in Germany.
Oh, and the id of accounts trying to access blocked sites are still available to the police without a warrant. It's just that instead of the data being sent by the provider to the BKA directly via a script, the BKA now has to ask for them. A process that can probably be scripted, too.
Earlier this month the minister chiefly pressing for the filter claimed there were 95 countries without child porn legislation. As it turned out in 71 of them all porn is illegal and the rest are in a state of civil war or just recovering from one and not exactly on a big pipe to the net. The minister however simply refuses to even listen, instead going around with he fingers in her ears singing LaLaLa at the top of her voice.
One of the countries she decried as a child-porn haven is India, which is now protesting over diplomatic channels. (Sorry, German again, but with some interesting source links: http://netzpolitik.org/2009/von-der-leyen-und-indien-antwort-der-botschaft/)
The good news: the filters are going to be implemented via forged DNS answers for now. A Youtube video shows how to change your DNS-Server from your ISPs to a properly functioning one in 27 seconds.