brotherhood_of_LAN - 1:49 pm on Jul 12, 2011 (gmt 0)
Looks like that's a defintive answer as to why the blocking is not working
I blocked all .ru visitors with 'deny from .ru' (since the only .ru visitors to my sites are spammers).
connection/lookup is slow or if it fails, then the user's request will also be slow or fail
If you are using (and are familiar with a scripting language, you could perform your reverse DNS lookups in the background via a cron, e.g. validate messages that are posted onto your site.