These "dictionary" attacks are tried against all manner of systems - FTP, SSH, Telnet (not that any system I run has this turned on, but...) and specific applications like phpMyAdmin and such.

I run a program called log-guardian (PERL) http://www.tifaware.com/perl/log-guardian/ (except I can't get in right now) that watches log files for patterns and performs an action if/when the pattern matches.

I have my system watching the "secure" log for ssh and ftp transactions - see more and bad passwords are "3 strikes you're out" - meaning the offending IP address is put into IPTABLES firewall to block any further conversations until the firewall is reset - typically every 12 hours.

The same can be done for web logs.

Note that this needs to be done at the operating system level so anyone with hosted applications will have a problem. On the other hand there are ways of doing similar things with .htaccess too.