Just by blocking a single IP, I managed to choke the amount of spammy comments on this blog to a minimum, zero spam comments to be honest.
An IP originating in Russia, from an ISP that can be described as non-responsive. I gave them about two weeks to resolve the issue, reporting the IP to them like an up-right citizen, got a immediate response and thought things will be sorted out, no such luck, days passed and I got tired of waiting, mailed abuse@<isp name>.ru and got the same exact answer back again, with the same ticket number as the first time. Waited another few days, nothing, the spam bot kept pounding my comment fields. Wrote them a new email, pretty much telling them that since they were so slow, I’d contact their up-link provider if it continues .. and it continues.
But, I don’t bother with it anymore, I just blocked the single IP and no spam comes through.