My hardware is a Apple 12 inch Powerbook G4 (1GHz PowerPC G4 processor), 512MB DDR SDRAM with a 56GB hard drive. I decided to make the upgrade from Mac OS X Panther to Mac OS X Leopard. I had been told that I would have to reformat my hard drive and install Leopard from fresh. I backed up the hard drive, and then decided to do the install over them top. After inserting the Leopard disc I run the installation application, and it essentially installed without any prompting. The estimate was initially 5 hours and this came down as it progressed. The installation ended in 2-3 hours and my Mac then booted into Leopard.
I was concerned about performance. Start up and shut down times are no longer, in fact I they seem to have improved since the installation of Leopard. General system performance is as good as under Leopard if not better.
Problems I experienced was that iDVD, iPhoto and NeoOffice no longer worked after the upgrade. I purchased iLife which fixed iDVD and iPhoto (iMovie still worked, and the new version did not install because it requires better hardware). I am pleased with the additional functionality of iPhoto, though I was slightly disappointed initially as it ran very slowly. However it seems to be fine now. A big positive of the new iPhoto is that the images rather than pixellated are initially blurred and then come into focus, visually this looks a lot better than before. NeoOffice needed to be reinstalled, after re-installing it now loads significantly faster than before, I don't know if this is down to the new version of NeoOffice, or the performance increase with Leopard.
Initially I found that Mail was a little buggy: specifically in relation to notes and to dos - at one point the same note started duplicating itself, then some of the to dos converted back into plain text, then the notes stopped saving updates. Therefore I have stopped using Mail notes and To dos, and use stickies. Have spaces allows me to have the stickies available all the time, which is much better then having them in Mail.
Features that I am really pleased with are Spaces (this is fantastic and allows me to have 4 screens worth of applications open at the same time and shift between each one. Press F8 to view the birds-eye view of the windows and drag applications between them, or drag the windows to the side of the screen and it will shift to the next door space. I usually have one space with my stickies in it, and one space with my email in, then use the others for internet browsing, coding, or iTunes. Time machine is fantastic, it is so easy and makes file backup fun. You can view finder in cover flow mode, this is a great feature, though I don't tend to use it much. Also dashboard is fantastic, but again I don't use it much. I like some of the changes to the look and feel, such as partially transparent menus.
Some people have criticised the new dock that goes on the bottom. I always use my dock on the right hand side, and this behaves as normal, so I am please with that. I think fans are a bit of eye candy, and not that useful. But expanding folders rather than opening the folder I find very useful, and have one for utilities, one for most used applications not on the dock, and one for all applications.
The main menu sadly is not transparent on my version - this is because of the age of my Powerbook, the graphic card does not support this feature. One of the other features that is great is previewing documents. Virtually all my documents preview, and almost all previews are instantaneous - this is fantastic, and so much quicker then opening the application. Also terminal is better, and allows you to add skins such as a translucent skin, which makes working in Unix look like something out of the movies.
Overall I think Leopard is great, performance is better, it looks better, and its got some great new functionality.