If my bank were to check the access logs of their online banking site, they’d discover a few requests every day with the following user agent:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.11 (actually 3.0b5 but a certain banking site won't let me in unless I lie about it)
Someone should tell them that trying to block people using user agent sniffing is about as futile as trying to reduce the teenage pregnancy rate by means of abstinence-only education.