This is my experience so far after 2 weeks using Ubuntu 9.04.
The boot time is really improved even if the hardware is not state of the art, the overall performance is very good as well. The stability is once again very good, I didn’t had any problems so far (crashes or system halting).
For me this is by far the best Ubuntu release.
This is currently my desktop:
Below are some links to customize your desktop.
Currently it’s very easy to install additional software (there are many pre-compiled binaries available for Ubuntu), if you want to do development you’re required to spend some time installing additional software, that’s also true if you want some additional media software or codec’s like mp3 support as well, but overall it’s a very simple and straight forward procedure.
Eva’s useful guide to Ubuntu 9.04
Essential Ubuntu 9.04 guides and manuals
Installing LAMP on ubuntu
Ubuntu Artwork
Have fun.