U.S. attorneys are appointed by the President, with the advice and consent of the Senate. Like cabinet members and most other high level posts in the Executive branch, they are political appointees; they are normally replaced en masse when a new president is elected, and are expected to help the President carry out the agenda he was elected for - within the limits of the constitution and the law, of course.
The Clinton administration at one point fired every single U.S. attorney at once without much remark. So why is there an uproar about Attorney General Gonzales and the Bush administration firing only eight out of the ninety odd attorneys?
One might think it's just a slow news period. There's more to it than that, though. It turns out the USAPATRIOT act contains a provision allowing the President to replace these attorneys with indefinite interim appointments - and since they serve indefinitely, he doesn't have to make the normal appointments that would need confirmation by the Senate. That removes the check in the system that keeps the appointments at least a little bit honest.
The other bit of controversy about Gonzales recently - that the FBI was overusing warrantless searches for information from phone companies and such - is also a problem with the USAPATRIOT act, whose provisions allowed those warrantless searches in the first place.
The fact is, the USAPATRIOT act is composed pretty much entirely of provisions like this. Half of them, like the warrantless search provision, are likely unconstitutional, and the other half, like the interim appointment provision, are at least unwise. The whole act, originally passed in the wake of the 9/11 attacks, is a perfect example of the folly of giving up freedom for security.