The third alpha milestone for Oneiric adds in Lubuntu as an official release flavor (Ubuntu with the LXDE desktop) as well as Ubuntu Core, which is a minimal root file-system for the ARM architecture.
Among the changes to be found in Ubuntu 11.10 are the Linux 3.0 kernel, more refinements to the (much-hated) Unity desktop, Ubuntu cloud enhancements, and much more.
Full details can be found on this technical overview Wiki page. There's also the mailing list announcement with more information and links to download the various flavors of Ubuntu. Ubuntu 11.10 final is expected in October.
Also interesting is that a few hours ago, Kate Stewart marked LP bug #760131 as being a milestone candidate for Ubuntu 11.10 Beta 1. This bug is for the main power regression introduced in the Linux 2.6.38 kernel as caused by PCI Express Active-State Power Management changes. There hasn't been a "solution" upstream in either the Linux 3.0 or 3.1 kernels yet since this is a tough problem. I'm not sure what Canonical is planning to do to "fix" the situation (considering their overall lack of low-level technical contributions particularly in the kernel area) besides possibly forcing PCI-E ASPM or just postponing the fix to a later milestone.