Good news, at least for now, though I expect an appeal will be filed and stop any reversal of the harm already done.

Via Washington Post:

Dane County Circuit Judge Juan Colas ruled that the law violates both the state and U.S. Constitution and is null and void. The ruling comes after a lawsuit brought by the Madison teachers union and a union for Milwaukee city employees. Walker spokesman Cullen Werwie said he was confident the decision will be overturned on appeal. “We believe the law is constitutional,” said Department of Justice spokeswoman Dana Brueck.

I'm reading through the ruling now, but the judge first noted that the plaintiffs (Madison Teachers Union and Milwaukee city employees) had the burden of proving the unconstitutionality of the statute beyond a reasonable doubt. Judge Colas then went on to rule that the limitations on collective bargaining for public employees violated the union's right of free speech, association, and equal protection, and voided those sections.

It appears from the ruling that this applies to city employees, but not state employees, since they weren't included as plaintiffs. I'm not sure how it relates to state employees, but am looking for more information.

This is just the first step in a series, I'm sure. By ruling that the US Constitution had been violated, I believe the union will have the right to take this case to a federal court, too. But I'm not a lawyer and I'll wait for one to weigh in on that.