Should Sources be Protected?

This question of course comes about because of the recent imprisonment of NY Times Reporter Judith Miller for refusing to give up her source in the Valerie (Plame) Wilson outing.

I am not asking whether or not it's right for Miller to go to jail but is it right to have a system where leakers are protected from prosecution due to "Freedom of the Press."

This question comes to mind because of this recent Time Magazine story where the following is stated:

In the future, the best hope for journalists may be a federal shield law, now in Congress, which would let reporters keep sources confidential under any circumstances. Thirty-one states and the District of Columbia have shield laws, while 18 additional states have similar protections. A federal law has been proposed by Senator Richard Lugar and Representative Mike Pence of Indiana, who have signed up dozens of co-sponsors. It's not that legislators love the media. But when it comes to advancing their politics, legislators can be world-class leakers and could have as much to lose as journalists.

So is it good to have a system where leakers are protected or not. Or does it have to be decided on a case by case basis?

I think I lean toward the case by case basis because then there is risk to leak but if the leak reveals a true injustice then it is difficult to argue it wasn't the correct thing to do.

It is an interesting question though?