Last week, a message on the Ubuntu Devel mailing list pointed out that Unity may not be default in Ubuntu 11.04 after all. After a long discussion, it was decided that Unity will be default, despite the split reactions towards Unity.
The reasons why it was considered to ship the Classic GNOME Desktop instead of Unity were various regressions but most importantly instability and frequently crashes. But it seems most of the crashes have stopped in the recent Unity versions and the remaining bugs will be fixed soon; and the regressions can be avoided: applications can still use the Systray if they are whitelisted and the Classic desktop is still available for everything else (remember: you can login to the classic GNOME desktop by selecting it in the login window!).
I followed up on the @ubuntu-desktop list to let people know that 11.04 was still slated to default to Unity, and to give people a chance to escalate concerns. [...] I do not believe any escalations have occurred or that the Desktop team has changed it's plan to default to Unity.
[..] The Desktop Team still feels strongly that Unity will provide the better experience for most users, is stable enough to ship, and will be more stable by the time final media is spun.
- Rick Spencer
You can read Rick Spencer's email @ Ubuntu Technical Board mailing list. There's also a list of official reactions to Unity (postitive/negative/neutral).
Thanks to Novatillasku for the news!