I am a Drupal newbie. I'm a professional developer, with good PHP experience and extensive ColdFusion background. I have built my own CMS in both PHP/MySQL and CF/MySQL, deployed probably 100+ sites on these custom web apps, and am just sick of being the only one who knows how to build/maintain them. I've spent more than a year researching, testing, exploring alternatives, including Mura, ExpressionEngine, Concrete5, EZPublish, WordPress (!), et al... and in the past 3 months have come convincingly to the conclusion that Drupal is where we want to go. Bought the O'Reilly book, met with several Drupal developers and picked their brains, and am very excited about diving in.
First project: This site will be a community site for dog owners, as a way of tracking information about specific pedigree lines (sire/dam/litter/etc). It will initially include at least 100,000 records about specific animals, and could eventually expand significantly beyond that.