I like the advice given above about making a bootable backup before choosing an upgrade path. I would like to add one vote for going to 10.5.8, which seems fairly stable, and considering 10.6 as a separate upgrade.
As a possible variation, one that is expensive in terms of the extra time that it takes, time when you cannot get 'real' work done on your computer is the following. The idea is to, crudely, "optimize" your hard drive by placing often used but rarely modified operating system files to the first sectors of your hard drive in addition to defragmenting them. Older defragmenters, e.g. Norton Speed Disk in Mac OS X 10.3, used to do this. Perhaps there are newer ones that do that now under 10.5, but I have not looked recently.
1.) Clone your computer to a bootable volume.
2.) Upgrade the clone, not your main drive, using the strategy of your choice.
3.) Boot from that clone.
4.) Test the clone. Do all of your key programs, data, etc. work.
5.) Make a go / no go decision. (You can make a second backup, if you have the resources and the time.)
6.) Using the latest version of Disk Utility, wipe and reformat your Mac's main hard drive. If you have time, you can choose the secure erase option to check the drive surface completely and swap out weak blocks.
7.) Using Carbon Copy Cloner (
http://www.bombich.com) in incremental backup mode, clone ONLY the System folder from your bootable clone to your main hard drive.
8.) Using Tech Tool Pro 5.0.5, (
http://www.micromat.com/) defragment your Macintosh HD once. This will defragment the System folder you just cloned.
8a.) Possible variation: requiring three defragmentations, next clone the Applications folder, (and the System folder too, even though the latter is already there, so that it is not deleted) and then defragment those two folders, before cloning the rest of your data in the next step
9.) Use Carbon Copy Cloner again, in incremental backup mode, to copy everything (or everything but the System folder; it should not matter if you have not made changes to the System folder). Now your new drive is complete.
10.) Perform another defragmentation. The System folder is already defragmented. It is already at the lowest numbered blocks on your drive. So it will be left alone by the second pass defragmentation.
Notes:
1.) You would think that cloning would automatically defragment (though not optimize) the target drive. But it does not. I believe that the reason for this is multithreading. The speed that this parallelism provides makes the copy faster, but at the price of fragmentation. If you are curious, you can clone a defragmented drive and then examine the fragmentation of the target drive. It's stunning.
2.) The Mac OS X installer does defragment installed files at the end of some installs. However, there is no regular global defragmentation.
Mark Frautschi