After six months of development Drupal 4.1.0 is now ready for some final testing. Drupal is currently in a feature freeze, and has been for quite some time, to make sure nothing breaks before the final 4.1.0 release.
If you have a Drupal site and you want to help testing, consider upgrading now. Anyone who doesn't have an old site and wants to help out can of course setup a Drupal site from scratch. All feedback is appreciated, good or bad.
Installation guidelines are available in the Drupal handbook. For bug reports use the project page, the mailing lists, the support forums or add a comment below. The release candidate is repackaged twice a day so make sure to download a fresh copy every now and then to get the latest fixes.