We suppose it's the principle of the thing, and on principle, TheSpecialist's new HDDHacker v0.5B really does let you use your very own HDD in lieu of Microsoft's $100 add-on number, but since Microsoft has firmly set the add-on HDD cap at 20GB (for legit Xbox Live-related usage), you won't be gaining much more than a moral win by following through with this hack. If you feel like really sticking it to The Man, you can use an 40GB 2.5-inch drive, but after running the hack it'll still show up as a 20 gigger for the 360's purposes. You'll also need the Microsoft enclosure to hook this up to your Xbox, so you might as well just fork over the $100 if you bought the Core 360 package and have been hankerin' for a HDD. Though, TheSpecialist seems to think the actual hook-up job shouldn't be too terribly hard for a competent hacker, so it really could be possible for you to drop a few bucks on a Western Digital BEVS Series drive (the only kind that works with the hack), copy the relevant sectors for a legit Xbox 360 drive, and have your very own Microsoft-free storage setup. The Man won't know what hit him.
[Thanks to everyone who sent this in]