So I've had Leopard running on my G5 for a few hours, and here are some thoughts.
Before I installed Leopard, I used Carbon Copy Cloner to clone my system onto an external FireWire hard drive that will ultimately become my Time Machine backup drive. This turned out to be a good thing, as the installation turned out to be a bit of a hairy experience. I initially attempted to do an Archive and Install, however during the process I got a message that installation had failed. I tried again, this time doing an Erase and Install, and got the same error. I dug out my original Power Mac G5 DVD and ran the Apple Hardware Test. Sure enough, it reported problems with memory. I pulled the two 512MB modules I had added a while back, reverting to the original 512MB of RAM. These modules were warranty replacements for my original pair which had gone bad, and I didn't really want to have to replace them again. Sure enough, this time the install succeeded. After the system was up and running, I put the extra memory modules back in and so far no problems.
During the install process, there was the option to copy my information over from an external hard drive; a feature I had used before when I replaced my iBook with a PowerBook, only this time I would be using just the hard drive rather than a Mac in FireWire target disk mode. The copy took a while, but when it was done I was up and running again, just the same as if I had done an Archive and Install -- except that the Previous System was tucked away on another disk rather than on the same disk. The only hitch was that it had trouble copying over the software for my Microsoft keyboard; I was able to grab that off of their web site and reinstall it without much difficulty.
Once I got things up and running, things seemed to work fine. I did have to update the Xiph QuickTime Components to get Ogg files to play properly in iTunes. One time Firefox got suck behind the other windows; quitting and relaunching fixed that. Chax doesn't work yet; while I no longer need it to get tabbed chats in iChat, I do miss having the buddy list automatically resize itself to be just long enough to show all my online contacts like Adium does. I'd use Adium for everything, except that I do use the video feature, and now expect to use screen sharing as well.
Thanks to a post on the InsanelyMac forum, I found the new nebula background that is used on the login screen. It's DefaultDesktop.jpg in /System/Library/CoreServices. I wanted to use it as my desktop, so I opened up the Desktop & Screen Saver preferences panel and dragged it into the little graphic well. Why Apple didn't just put it in with the other default desktop pictures, I'm not sure.
I like the look of the new dock. Until now, I'd always kept the dock set to hide unless I moved the mouse to the bottom of the screen. Which probably made sense back when I was using a 17" CRT (at probably 1034x768) like when I first installed Mac OS X 10.0. Since I'm now using a 21" LCD at 1600x1200, I think I can give up that little bit of space at the bottom. I'm not sure about the Stacks thing but I think I can get used to it. In the past, I've kept a copy of my Applications and user home folder in my dock for easy access. I'd right click on Applications to pick an application, and usually just click the home folder to open it in a Finder window. It seems to be taking a bit longer to find applications in the grid view than it did as a menu, since instead of just finding it vertically, I have to search both the right row and column in the grid. On the other hand, not having to scroll ought to be nice, so it balances out. I do prefer the grid view to the fan view; having the list curve off to the side seems rather useless.
I'm not wild about the new folder icon; I prefer the older ones. The new ones remind me of the rather ugly ones used in the default Fedora 7 desktop. Did someone decide that the 3D folder icons--which date back to the Copland project and ultimately appeared in Mac OS 8--have gone out of style?
I also saw some complaints about the transparent menu bar, but that doesn't seem to be bothering me. It seems pretty smart: Against a dark background, it is less transparent so it maintains good contrast with the black text.
I'm not wild about having document icons be previews. I usually turn this off in Konqueror. I normally use the column view, so all the icons are pretty small and they all look about the same. I'd much rather have a Word document icon for .docs, an Adobe Reader document icon for .pdfs, and so on, and use Quick Look to get a preview.
I'll wrap this post up with this thought: How come I haven't seen any Leopard Lolcats yet? Too obvious?