With the first Alpha of Ubuntu 12.04 LTS unleashed to testers worldwide, Canonical decided to change the official release schedule for the upcoming Precise Pangolin distribution and remove the Release Candidate version!
From the official Ubuntu 12.04 LTS release schedule it looks like the Release Candidate version, which was supposed to be released on April 19th, 2012, is no longer present. This is now the current release schedule for Ubuntu 12.04 LTS (Precise Pangolin):
February 2nd, 2012 - Alpha 2 release
March 1st, 2012 - Beta 1 release
March 22nd, 2012 - Beta 2 release
April 26th, 2012 - Final release of Ubuntu 12.04
Looks like no other development version is affected by the removal of the Ubuntu 12.04 LTS Release Candidate, and the date for the final release of Ubuntu 12.04 LTS remains intact - April 26th, 2012.
Being an LTS release, the Ubuntu 12.04 will have at least four regular maintenance releases. The first one, Ubuntu 12.04.1, will be released in August 16th, 2012; the second one, Ubuntu 12.04.2, will be released on February 7th, 2013; the third one, Ubuntu 12.04.3, will see the light of day somewhere in mid summer 2013, and the last one, Ubuntu 12.04.4, on January 24th, 2014.