Well, currently I just installed Jaunty, and it seems to be okay. I'll start off with the installation.
It was rather straightforward. I used the install option rather than booting to the LiveCD desktop. First thing you'll notice is the installer is full screen. As well, they also fixed the partitioner. It now shows the disk properly, and the more partitions you make it works correctly, rather than going off screen. I chose Ext4 as the default FS, and it's okay, but more on that. It took a grand total of 15 minutes to install, the fastest I've ever seen it yet.
The first boot was fast, as are all the subsequent boots. My 1.6Ghz, 512Mb Ram craptop boots in 30 seconds flat now. The login screen is very nice too, revamped and more modern.
I started by moving my backups onto my drive -- 115GB of video, music, and games. It worked fine. I installed a list of applications that I find standard -- mplayer, smplayer, gcc, build-essential, and of course, armagetron. They plus 300+ other MB of download files installed correctly.
The menus are snappier, gnome notification is much more professional, and everything is generally more responsive. After I added all the repos and did 'sudo apt-get update', then ran hardware drivers, it picked up my broadcom just fine. Everything just works.
However, there is a problem. Ext4. Don't install this if you want a stable computer. Removing things to your trash is safe, but don't be doing anything essential if you're emptying it. Deleting files can hard-lock your pc. Even "<ctl><alt>REISUB" doesn't work. It requires a hard boot. Stick with Ext3, but if you were unlucky enough to install 4, there will be a patch in about a month, so it's not forever.
The update manager went through some changes. Only once a week it will notify you about an update for files, and it will notify you immediatly if it's security related. However, if you close it when it's security related, it comes back right away -- very annoying. This is changeable, but I haven't gotten around to it.
Overall, besides Ext4 and the UpdateManager, I haven't many complaints about 9.04. Installs quick, apps just work, and everything seems to be nice and dandy. I recommend it to anyone. Good job Canonical.