So far the leopard experience has been amazing. Tiger was the first Apple OS that I used full time, and I did enjoy it. After upgrading to leopard though - all I can say is: amazing. Stacks, the new dock, time machine, tonnes of awesome new features. If you are planning to upgrade, do it now.
Finally Java Support
I would have upgraded right when the OS came out, but from what I heard it didn't support Java 1.6, which I need for school and to run my various projects. Java 1.6 can be downloaded from the Apple Developer Connection website, and runs about 75MB. From Apple:
Java SE 6 Developer Preview 8
Apple has recently released a new developer preview of Java SE 6 for Leopard via the Apple Developer Connection (ADC) site at http://connect.apple.com.
The Java SE 6 release for Leopard is targeted at Java developers. This version of Java for Mac OS X requires an Intel-based Mac capable of running 64-bit applications, including computers with Core 2 Duo processors and any Mac Pro computer. Java SE 6 takes advantage of Leopard's 64-bit capabilities to offer unique performance capabilities for current and future generations of Macs. Please see the release notes included with the Java SE 6 download for additional information about this preview release.
When I saw this I was so happy that I could finally upgrade to leopard. I backed up my stuff and it was onto the install.
Installation
I put the leopard DVD onto a partition on my external hard drive, so the install went really fast. It was smooth and in about 15 minutes I had a fresh install of OSX Leopard. There were no problems, and even my bluetooth mouse was automatically detected. By the end of the installation, I was really impressed.
Post-Install
I was a little bit worried that the programs that ran perfectly on tiger would not run on leopard. Well, so much for that - everything runs perfectly. It seems like things are even running faster than with tiger, and certainly faster than windows. I have absolutely no complaints about leopard, and I hope I don't find anything too big that makes me hate it because with these features I don't think I could use anything else.