While there aren't many changes yet for Ubuntu 11.04, one of the first changes is that GCC 4.5 will be the default compiler version used by this next release, compared to GCC 4.4, which was used by Ubuntu 10.10 and 10.04 LTS. There's also two less maintained Ubuntu architectures this time around.
Next week there is the Ubuntu 11.04 Developer Summit to discuss some of the features and plans for this next release due out in April. Ubuntu 11.04 will have a greater focus on performance testing, an X.Org Server not running as root, GNOME 3.0 packages, Btrfs file-system improvements, and many other changes. Ubuntu 11.04 is likely to ship with the Linux 2.6.37 kernel.