When I tweeted the above comment - I was quite appalled at how slow iTunes was at delivering content - someone pointed me to this post on Daring Fireball that says the fix is to not use Google DNS. There are similar complaints in the OpenDNS forums. The tweeter speculated that if I was using OpenDNS - and I was - it would have the same impact. I downloaded Tapper World Tour HD from the iTunes store and it took 3 minutes 36 seconds to grab the 193 MB file. That's 890 KB per second on the download, and my connection is capable of just over 3000 KB/s. If there was one thing I'd expect/hope to deliver bandwidth-saturating results, it would be a content deliver network such as iTunes.
I went into my router, set the DNS back to my ISP (Shaw), and rebooted the router. On my computer with iTunes, I did an ipconfig /flushdns, along with a /release and a /renew just to make sure everything was reset. I verified the computer wasn't using OpenDNS, then I started up iTunes and re-downloaded the same file. It downloaded in 3 minutes 2 seconds. A slight improvement, but not much and frankly within the margin of error for a test like this.
I'd like to ask the Apple Thoughts community if they've seen similar results with OpenDNS or Google DNS, and if stopping using those services resulted in a significant speed boost on downloads. Also, if my methodology was flawed in some way, I'm happy to learn how to better test something like this.