2007/08/14 0.8.1 is now available and fixes some security issues in the default configuration files and includes new filters and actions. The "mail" actions are now deprecated and should be replaced with "sendmail" actions. fail2ban-regex now accepts "ignoreregex".
2007/06/07 Daniel B. Cid wrote an article about Attacking Log analysis tools. There is a section that points out a vulnerability in Fail2ban. I strongly recommend that you apply the patch provided in the article. A few weeks ago, Yaroslav Halchenko wrote an article about Fail2ban for Debian Package of the Day.