I’ve tried to use Nagios 3.0 b2 but there was a problem with the mail, this was corrected with a new beta release. You should download it if you were using the beta 2 version
The new realse of Nagios 3 was released today. It fixes some bugs and add improvments to the new host logic check.
As soon as the new version will be available, a tutorial will be published about Nagios 3.