I just wanted to share with the community that Diana (build 9821) looks very good after installing Ubuntu 9.04, Java 6 (build 13) and installing the AA hack plugin (makes fonts look marginally better).
Being a huge look-and-feel guy, I wasn't too thrilled with the overall appearance of IntelliJ under Ubuntu 8.04 and Java 6 (not sure what the previous build # was). The appearance is now definitely good and is no longer a hindrance. I'm using the monospaced font (size 13). I'm attaching a screenshot.
On the whole, anti-aliased fonts look truly fantastic in Ubuntu 9.04. I guess it means that I won't be buying a Mac anytime soon ;-)