For example, yesterday iTunes started up and hung with a SPOD (spinning beachball of death). I killed it, restarted -- same problem.
Did a safe start (shift on startup), tried again -- same problem.
Disconnected the ethernet cable -- same problem.
Oh, wait. The lights on my USB hub look odd ...
Remove my iPod shuffle from its cradle. Problem resolved. Turns out the Shuffle went through a laundry cycle, but somehow enough remained to cause iTunes to hang on startup. No more shuffle -- I really disliked Shuffle 2.0 anyway (insanely stupid that it didn't charge/sync via a standard mini-USB connector).
Maybe safe mode would have helped me figure this out sooner.
Probably not, iTunes safe mode (hold cmd-opt on start iTunes) only turns off plug-ins. Searching on it, however, led to me to a list of iTunes Mac 7.6 Help: Keyboard shortcuts such as:
- cmd-opt: safe mode
- space bar: stop/start (great one)
- cmd B: hide/show artist and album columns (handy to see more without horiz scroll)
- cmd R: show song file in file system
- cmd L: show currently playing song in a list
- cmd-opt as you connect an iPod/iPhone (hold until device mounts): prevent an iPod from automatically updating when you connect it to your computer. 
- option-click list: reshuffle
- option-delete list: Delete the selected playlist and all the songs it contains from your library
- option-click the top-left round green window (+) icon: instead of switching to a mini player, the iTunes window adjust to an optimal size for the current display. In other words, it behaves like the green icon on every other OS X app.