I'm using the Radiant content management system to build a site for a client, and I'm loving the newly released version 0.6. The new extensions support is an excellent way to add bits of functionality to your site, and I'm using them for the contact form, getting a quote via email, and a custom gallery. There's one little gotcha, though, with using the mailer extension (from the Radiant SVN repo): it won't send mail from a default Radiant install. Luckily, the fix is easy.
It took me a few minutes to track this down, as I never specify the list of frameworks I'd like to remove in config/environment.rb. I probably should, since I never use ActionWebService, but I just never end up doing it. Well, Radiant does, and it includes ActionMailer in the list of frameworks to not load when starting the application. So, if you want to send email with the mailer extension in Radiant 0.6, you need to edit config/environment.rb and remove action_mailer from the list of frameworks that are skipped:
config.frameworks -= [ :action_web_service ]
Other than that little snag, working with Radiant has been fun, and I'd recommend it to anyone as a starting point for a custom site.