They don't take no for an answer

My experience is that blocking spam generated by a botnet is rather unwise to say the least.

Blocking or putting a delay on *.ru, *.pl etc will result in 10,000 random hosts accross the world re-trying and eating up your SMTP server's capacity.

I have found that it is best to let it in and quietly kill the spam with SpamAssassin. I got a 90% reduction in bandwidth doing this.