I can't figure out why the government just doesn't remove the hard drives and send them to a shredder. Even a private individual can achieve roughly the same level of security with a drill and a 1/2" drill bit. With the
price
of drives being what they are now it can't impact very much the resale
value
of the computer to sell it without a drive installed.
Shredders don't like metal, but there are things that'll make quick work of a drive: http://www.networkworld.com/news/2006/062706-guard-dog.html
The Air Force seemed to think a 1-2 punch was in order, according to Cryptome: "2.5. Destruction. It is a good practice to sanitize media before submitting it for destruction. Media may generally be destroyed by one of the following methods (see Table 2.1). (*NOTE*: Although approved methods, options d and e use acid, which is dangerous and excessive, to remove recording surfaces. Options a, b, and c are recommended over d and e.) " http://cryptome.quintessenz.at/mirror/afssi5020.htm
-Sean