I suppose my first question to you would have to be: how many albums do you have of Collective Soul, Dave Matthews, and Tom Petty? More albums means more of a chance of a back-to-back. Also, some "greatest hits" albums can be longer than others (IIRC, Tom Petty's Greatest Hits has far more than the 12 tracks Tony's been messing with). The other piece of information is how many total tracks are you shuffling when you get this behavior?

Just plaything the program a bit I do notice quite a few back to backs, though this is generally with artists who have more than one album. If you weren't shuffling too many tracks (we've been talking around 3000) this would also change the test. You might just want to play around with it and try plugging in some numbers you think represent your data. Though back-to-backs don't get highlighted, they are still easy to see. Of course, the program doesn't show back-to-backs from multiple artists on the same grid but I still think you might be able to tell what kind of behavior is reasonable.

As for me, I typically don’t see any of this behavior because of how I’ve structured my playlists. In fact, I hardly ever use “shuffling” at all. Instead I have a special playlist that picks a single song at random from 14 artists chosen at random, and then repeats the process a dozen times or so. This effectively circumvents the “clustering” and “back to back” behavior we’ve been talking about.