After a few days of working with Ubuntu 9.04, I have two comments to make about it - one positive and one negative.
On the positive side, the release notes say that they improved handling of multiple displays, and they really have done that. This is something that has been important to me, because of the way that I use my primary laptop, for quite some time now. In Ubuntu, it has basically gone from not working very well (or at all) in 8.04, to working quite well in 8.10, and now to working extremely well in 9.04. I have tried it with both my Lifebook S6510 (Intel 965 display controller) and my Lifebook S2110 (ATI Radeon Xpress 200 display controller), and both of them handle two displays, not mirrored, just fine.
On the negative side, I'm not terribly pleased with the way the Ubuntu Update Manager works with the new notification system. When there are updates available, all that happens is that I get a very brief flash of a window on the screen, which immediately minimizes (disappears from the display and is only present in the panel icons). There are plenty of ways that I can not see that window flash past, ranging from simply not paying attention, to not even being at the screen when it happens. Now, add to that the fact that I always auto-hide the panels, so I don't see it down there right away either. The result is, I'm not aware that there are updates available until I shut down, when the Update Manager window once again flashes onto the screen briefly before the screen goes blank. It seems to me that the obvious solution is that the Update Manager window should stay open, rather than iconify, but I can't find anywhere to set this.
Anyway the bottom line is, if the only thing I have to complain about after a week of use is something as trivial as this, Ubuntu 9.04 looks like a very solid release.