I'm going to quickly jump in with a link to alt.usage.english which has a discussion on this subject:
http://www.faqs.org/faqs/alt-usage-english-faq/

The discussion closes with the following:
Hardly any serious commentator believes that infinitives should never be split. The dispute is between those who believe that split infinitives should be avoided when this can be done with no sacrifice of clarity or naturalness, and those who believe that no effort whatever should be made to avoid them.