5th
Don’t, really don’t
Do not upgrade to Mac OS X 10.5, at least not now, unless you have really nothing else to do. Wait maybe another six months and make sure to take a week off then, you will need it. Not that 10.5 is in any way a particular problematic update but you will probably find about half a dozen minor issues and each will take about a day to fix. That is why you need that week, and a box of tranquilizers. And hopefully they have fixed one or two of these half dozen issues by then.
Apple may manage to fix in the order of about 100'000 bugs in a major OS release but they also may introduce about new 100 bugs (remaining after the .2 release) and out of these 100'000 fixed bugs one notices possibly ten, but out of these 100 new bugs one also notices about ten. That is the truly amazing part. To give you just a few examples. In Tiger, only a few Adobe apps would not hide with cmd-h (but they would hide if alt-clicked on another app). In Leopard, half of the time when you try to hide an app it will not hide, not by any method. Restarting the app will bring back the hiding capabilities. Or take mounting a server, in Tiger one authenticated ones and that was it for the rest of the year, in Leopard one has to authenticate about every second time, it is pretty random. And the server used to appear in the sidebar, now it may appear or it may not.
All these are rather minor issues but one spends hours first mounting and unmounting servers trying to figure out what is happening and then scouring the net for any indications of what is going on. That is why you need a week to install Leopard. And if during every month waited one issue is fixed then every month waited might save you one day of your life (and possibly even a few weeks of your life, considering the frustation that is avoided).