An update to the Ubuntu 11.04 installer (Ubiquity) finally brings upgrade support to the Ubuntu Live CD. That means that for instance if you use Ubuntu 10.10, when you'll boot the Ubuntu 11.04 Live CD you'll have an option to upgrade (without losing your documents and installed applications). Besides this change, there's also a redesigned partitioner:
(here's another screenshot, but in this one the 'install alongside' option is missing for some odd reason)
Because this has just landed in Ubuntu 11.04 (and because Ubuntu 11.04 is still in alpha!), it's best not to try this feature yet as it may break stuff (I didn't tested it).
For more Ubuntu 11.04 Natty Narwhal news, browse our Natty development tag.