The world's current most popular Linux desktop flavor, Ubuntu, is busy at work on the successor to their existing version, which was released only a month ago. The next update, Ubuntu 9.04, is currently under development and should have an alpha version available for perusal this week, perhaps even tomorrow.
With the 9.04 release, the development team has mentioned numerous features they are bringing to the table. One of the biggest on that list is improved boot time, seeking to optimize the boot process at both a kernel level and a service level. That change, along with some large improvements planned for power management, indicates that Ubuntu sees the mobile market as a key place for growth. That is particularly true for devices like Netbooks and other MIDs, where embedded Linux is proving to be increasingly popular.
The actual release is not expected until at least April. Ubuntu is made primarily by the feedback they receive from their users, though, so if you like to experiment you'll have a chance to get the alpha very soon.