Because of the continuous incursions of spammers and their painful comments with relative URL of medicinal and casinos that I don't truly accept anymore, I'm near to decide to use the commenting feature of Movable Type 3 (installed yesterday ) that only who is registered can comment. From the manual:

This means that the first commenter records in, from the second is ok. And for the spammers should be beautiful difficulties. But I must still understand well how the reader records before the time on Typekey.

I do not see valid alternatives. That is, there would be that one to moderate the comments, but for me it's not valid: the comments work 'cause they are immediate, recent - the date of comment is part of the same comment, it means reactivity to the argument, interest, or chance.
In any case, I have tried: are months that I'm holding open comments and in the last weeks I make a rebuild too often in order to cancel recursive comments spam.
If someone knows how to avoid these hateful spammers continue to infest blogs face me know...please (what about MT blacklist on MT 3.x?)