One really important thing I forgot to mention about Leopard: DO A CLEAN INSTALL.
But before you do anything... do a complete bootable backup of your hard drive. Please! I beg you! Doing OS upgrades on a computer is the way to guarantee something will go horribly wrong if you aren't backed up. So go to your local computer store, Apple Store, or your favorite online retailer (my favorite for Mac stuff is Other World Computing) and buy yourself an external drive to back everything up first. You will be glad you did.
The first machine I installed it on, my MacBook, didn't take to it too well when I did the install as an update. In fact, my poor little MacBook didn't do well at all. It got slow, buggy, things crashed, it had problems booting, problems shutting down and was not much fun to use. You would be in the middle of doing something and all of a sudden the fans would come on and the Activity Monitor would show all of these strange (meaning not the normal processor intensive things going on behind the scenes) processes running at nearly 100% of the laptop's capacity.
So after a couple of hours of trying to track down what caused all these issues (although deep down I knew it was because I tried running the update) I then heeded the advice of Apple and did a clean install... and it worked great.
At times, I don't learn lessons easily, however. So my next Leopard target was the Mac Mini in our family room that is used by my wife for surfing, my son for playing Lego Star Wars and Wingnuts and my inlaws for watching Korean soap operas while they are hanging out with the twins. So what did I do, why I tried running the upgrade again on the Mini.
How did it work?
Horribly! I had everyone mad at me because it actually seemed (to me) to work pretty well after it had finished. Now I don't use the Mini much, unless it requires some sort of fix, so I guess I didn't spend that much time checking everything out, but I probably should have. Safari started crashing, Nick (my Lego Star Wars loving son) was unhappy because the games wouldn't load and my inlaws couldn't get any of the online videos to play. Lets just say my family was not seeing the value of upgrading to Leopard.
So again, I got the various install disks out and did a clean install and it worked great. No problems whatsoever.
Now I have to confess, in the past, I have gotten away with doing upgrades (I did 10.3 to 10.4 upgrade on my 15" Powerbook in a hotel room in Ohio somewhere after a shoot) and then came home and did the same for all my other Macs and it worked fine... that time. But Leopard seems to introduce enough new stuff that upgrading can cause more problems than just spending an hour or two and starting fresh.
The other good reason to do clean installs is because it gives you a chance to do some spring cleaning on your computer. You actually look at how much junk you have installed on your computer vs. what you actually use all the time.
Some people that are too scared to wipe their hard drive (or maybe they just like living dangerously and are opposed to backing up ) like the archive and install choice. That is where it moves everything on your computer into a folder called "Old System" or something like that and installs the new system in a new system folder. The reason I don't like this is because it leaves all your applications alone and there are a number of apps that put stuff in other places (that is now called "Old System" ) and so the temptation is to start using the stuff in the old system instead of reinstalling your apps, too. Take this as a fact... if you try to use your apps from the previous install, you will spend more time trying to figure out why they aren't working right than if you had just installed them cleanly in the new system.
After doing the clean install, this is when you can go to your backup of the drive to import thing like your email, preferences and other odds and ends that you are going to need on the new system after you installed all your apps.
Another thing that I would suggest before doing the upgrade is make sure you have all of your downloaded installers, installers on CD's or DVD's and most importantly, serial numbers for everything before you do the reinstall. I actually print out a copy of what is in my applications folder so that when I do the reinstall I don't forget anything important. I actually create a folder with the latest drivers and installers when I did my upgrades on all the machines so I could just work down the list in the folder installing one after another which saves time of having to hunt for disks and downloads later on.
I would also suggest doing a Google search to make sure that all your critical applications and hardware (printers, scanners, etc.) are working with Leopard. In Google just search for the name of the hardware and "leopard" or "10.5" or search for it both ways. You can also include words like "issue, "problem", or "conflict" to see if anything comes up.
If it turns out that your printer or some other hardware is not Leopard compatible, look at the bright side... you really do deserve some new peripherals, don't you???
