This is not really a hint of mine; it is blatantly stolen from this discussion over in the Apple Discussion forums.
When using iTunes5, you may have noticed that sometimes album shuffle does not work (i.e. it works as song shuffle instead), which is a nuisance if you're listening to something like classical music.
The solution is simply to put the slider for smart shuffle exactly back in the middle of its range -- the slider is in the Playback section of iTunes' preferences. Hardly a feature, I guess...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050915105151281