Da Hammer of Justice: By the way, in all the courtrooms I've ever been in (usually as a lawyer, mind you), I've never heard or seen a gavel used. This is purely a device for t.v.
Miller does not have a right to withhold her source from the Grand Jury. Grand Juries, for those of you unfamiliar, are the most scary judicial bodies in existence. They serve with an all-powerful ability to compel testimony and evidence. You, as a witness, have almost no right to refuse to testify, no right to counsel, your 5th Amend rights aren't explained or really even acknowledged. If indicted, the prosecutor pretty much can hide the evidence that would otherwise tend to call your guilt into question.
The key distinction to be made is that you're not being found guilty of anything; only that there is a prima facie case being put on that suggests the indictment should stand pending trial.
The ABA tried a while ago to re-introduce some civility into the process, and return the grand jury to what it was supposed to be, or a "bulwark" between the government and you. If you've followed any of the federal cases of late, this Miller one only being the most noteworthy example, you'll see how little credence the USDOJ tends to give the ABA.
Miller, while not being indicted, has refused to testify; not on the grounds that she might incriminate herself, but that she doesn't want to give up her sources. The argument is that the press will be chilled if it cannot interview people because they are afraid of themselves being indicted based on what they say to the press. This would be poignant in typical "whistle blower" cases, where indeed, you want people to speak out against corruption, etc.
However, the Government's case is equally compelling: just because someone, who did something illegal (or potentially so) tells a reporter details of that crime, doesn't mean that the reporter can withhold the details from a grand jury, which is empowered with broad investigatory tools. Disobeying a subpoena from a grand jury is tantamount to contempt, hence Miller's dilemma.
You can say it's noble, and it probably is, but harboring a criminal who gave you an interview isn't the best defense I've ever heard. Especially when you're making money off of that information, tooting your own horn in the process. It is not analogous to a priest taking confession, or something of that nature.
Of don't cry for Miller too much. She's got a nice book deal in the works out of this one. Count on it.