Re the site getting kicked off the server for 1 spam attempt per second – that’s extreme, and shows that the host didn’t know what it was doing, at least to some extent. I haven’t tested this out, so I’ll pull my head in if required, but I can’t imagine that a simple spam block should consume much resource. Perhaps they were doing an Akismet check (possibly resource-heavy) first and putting something else in front of that might have knocked off much of the attempts. I do remember hearing somewhere else that changing the comment form name was enough to knock off spam and that’s a neat trick; there are some similar things that can be done with MX records to kill off spam (‘nolisting’).

There are some nice free firewall products available now which should block such attempts automatically (CSF); mind you, I’m not sure if they do, but it could save a server quite some CPU time if it was able to proactively firewall such IPs.