I say this every time there is a major os x revision, but I think I’ll say it louder this time. If you’re upgrading to tiger, back up your home directory and other essentials, and then:
DO A CLEAN INSTALL
Seriously, just do it. It will probably be more work, but trust me, it’s worth it. How would I know, anyway? Aside from working in and around Mac OS X all day every day, I also help moderate a Mac OS X IRC channel. *Every time* there is a major release, there are *always* streams of people who come in with issues that would have been averted had they done a clean install.
Yes, in-place upgrades have been a supported installation method in OS X for a long time. No, windows does not make you do a clean install either. Yes, upgrades work fine for some people. Still, do it clean. In the parlance of the Mac OS X Installer, this is the “erase and install” option.
There are two other hidden advantages here. One is that it forces you to back up your data at least once per major release; another is that you get your primary drive defragged (which can have positive performance impacts, especially if it’s been a while since the last reformat). One way to keep yourself from having filesystem problems is to reformat once every year or so. Major release time is a perfect opportunity – think of it as preventative maintainence (yes, it means you don’t need to shell out for DiskWarrior or whatever. On that note, by the way, you really shouldn’t use disk utility software against tiger volumes unless they have been specifically upgraded to support tiger).
More info is about installation options is available here: