[ghulse]

In the most recent issue (911), Ryan Kinrade asks if there is a way to make the iPod Shuffle treat playlists appear as individual tracks. Far be it for me to question why anyone would want to do this (What's wrong with playing Ella Fitzgerald next to Queens of the Stone Age, I say), but I think I have a much easier solution if what you really want is not to have different styles of music clashing with one another.
Using the Autofill function, and unchecking the button "Replace All Songs When Autofilling," you can create contiguous blocks of songs that are still randomly selected from different playlists.
Start by Autofilling your Shuffle from your Jazz playlist, for instance. Then, select two-thirds of the tracks just copied to your Shuffle and delete them. Yes, that's right, delete them. Then do the Autofill function again, this time selecting from your Classical playlist. Then delete roughly half of those tracks, and repeat the process using your Classic Rock playlist. When you're done, you will have contiguous blocks of like songs, selected equally from your Jazz, Classical, and Classic Rock playlists. If you're not in the mood for Jazz, you can skip tracks until you get to the Classical selections, or skip ahead still more until you hit the Classic Rock tracks. And don't forget to to set your Shuffle to "Play in Order" mode. You can even move entire blocks of songs around if you want. For example, you may decide you want the Classic Rock selections to be first on your Shuffle playlist. Just select those songs within iTunes, holding the Shift button down, them and move them up the list.
The beauty of Autofill is that it preserves the order of the songs. In this same way, you can use the Autofill function to randomly select songs from your library, and then by deleting a portion of them to make room for the new Decemberists release, for example, you can then hear that album in the correct order, and have it followed by a random selection from your library. Works like a charm.