While we have had tentative release schedules for Ubuntu 11.04, Ubuntu 11.10, and Ubuntu 12.04 LTS since last May when the Ubuntu 10.10 release schedule was reworked to allow the Maverick Meerkat to be released on the 10th of October (to make Ubuntu 10.10 a release on 10.10.10), the Ubuntu 11.04 release schedule is now fairly firmed up and it is set to be greeted into the Linux world on the 28th of April in 2011.
The Ubuntu 11.04 Alpha 1 release is coming quickly on the 4th of November -- less than a month after the release of Ubuntu 10.10 -- followed by a second alpha release before ending out the year. There's a total of five alpha releases planned for Ubuntu 11.04 before it reaches beta on the 31st of March. A release candidate of Ubuntu 11.04 is expected on the 21st of April and then it will officially be welcomed into the world on the 28th of April. The Ubuntu 11.04 release schedule can be found on the Ubuntu Wiki.
Ubuntu 11.04 will focus on further polishing the Linux desktop experience, provide greater support for ARM-based devices, an enhanced mobile experience such as those with multi-touch support, it may use the Btrfs file-system by default, is likely to ship with the Linux 2.6.37 kernel, X.Org Server 1.10 integration, and should ship with the GNOME 3.0 desktop. Many more features for Ubuntu 11.04 will be known in the coming months.