This bug report which was reported yesterday suggests that Lucid was about to ship with an issue that caused the secondary operating system to be missing from GRUB when installing in a dual boot setup; if migration assistant found anything to import.

“When installing in a dual boot environment, the other operating system will not appear at first in the GRUB menu. Installing the available updates and rebooting will fix this issue.”

Potentially catastrophic to Windows and Mac users who want to install Ubuntu alongside their current OS, thankfully the bug has been fixed in updates and a decision was made to re-spin the ISO images for the Ubuntu desktop edition only to include the updates in time for release. Other variants will get the update in the next day or two (or should already have it).

The comments on the bug report give an excellent insight into the stressful situation key developers and Canonical employees face around release time, and we should all +1 them for picking up on this only hours before release and fixing it swiftly.

Any help on testing the fix would be much appreciated, but please DO NOT bombard the bug with pointless comments at such a crucial time.

“We’ve decided to respin the 32bit and 64bit CDs of Ubuntu Desktop *ONLY*, as we feel this gives us the widest spread fix possible and allows us to still release today (April 29th). Unfortunately, this means other affected variants, such as Xubuntu, will not have this fix, and we deeply apologize for this.”

We’re intending to have this bug fixed in the official ISO release at this point.”

— Robbie Williamson – foundations team

More info here.
bug grub2 lucid ubuquity