We knew some of these changes were coming. Mark Shuttleworth, Ubuntu's founder, had already announced that Ubuntu would be moving from OpenOffice to LibreOffice for its default office suite. At this point, LibreOffice is 99.9% identical to OpenOffice. By the time Ubuntu 11.04 is released in April, LibreOffice is expected to have improved performance and increased interoperability with Microsoft Office 2007 and 2010 formats.
Some people had expected to see Ubuntu switch from Evolution to Mozilla Thunderbird for e-mail. That did not happen. Although many dislike Evolution -- I've never understood this myself since I like Evolution's do-it-all functionality -- it was decided that Thunderbird simply wasn't ready yet.
I'm not sure Thunderbird will be ready anytime soon. Although I was a Thunderbird supporter early on, the Mozilla Foundation hasn't spent much time or effot in keeping Thunderbird up-to-date. The two main reasons why the Ubuntu programmers have deferred making Thunderbird the default e-mail choice are it's lack of a built-in calendar and no Microsoft Exchange support. There were also my main problems with Thunderbird last year.
If you want a better, full-featured e-mail client in Ubuntu, my suggestion is to start working on cleaning up Evolution. I don't see Thunderbird taking its place.
The most controversial change, other the switch to Unity for the main interface, is that Ubuntu is changing its default music player from Rhythmbox to Banshee. Personally, I welcome this move. Banshee is my favorite Linux music application. As I said when it was first introduced in 2006, Banshee is as close as you can get to an iTunes for Linux. I still think that's true.
While some people love Rhythmbox, and other music players like Amarok and Clementine have their fans, Banshee's biggest opposition will come from those who hate that it uses Mono, the open-source version of Microsoft's .NET infrastructure. For some people, the mere presence of Mono in a Linux distribution endangers it from Microsoft software patents taxes.
I don't think that's the case. Software patents are an evil that, as the current mobile phone sue-me, sue-you circus shows, don't require the explicit use of a named technology. Besides, Mono users and developers already have Microsoft's blessing. You may dislike using a program built on top of a Microsoft technology, but I don't see any special legal danger in using it.
In any case, if you really can't stand Banshee, Unity, or LibreOffice in the forthcoming Ubuntu, you'll still be able to switch back to Rhythmbox, pure GNOME and/or OpenOffice. Personally, I'm looking forward to Canonical's new take on the Linux desktop, but if you can't stand it, you can have your desktop your way. After all one of Linux's beauties is that you can always set it up just the want you want, not how someone else wants it to be.