As noted the Supreme Court struck down limitations on campaign advertising in a challenge to the McCain-Feingold Campaign Finance Reform bill. From The Hill McCain has now responded:

It is regrettable that a split Supreme Court has carved out a narrow exception by which some corporate and labor expenditures can be used to target a federal candidate in the days and weeks before an election,” McCain said. “It is important to recognize, however, that the Court’s decision does not affect the principal provision of the Bipartisan Campaign Reform Act, which bans federal officeholders from soliciting soft money contributions for their parties to spend on their campaigns

The court weakened a provision in the law that strictly limited ads paid for with corporate and union money within 30 days of a primary and 60 days of a general election. It ruled that the law violated the First Amendment rights of Wisconsin Right to Life, which was prevented from running ads urging voters to contact Democratic Sens. Herb Kohl (Wis.) and Russ Feingold (Wis.) about a filibuster of judicial nominees.

McCain-Feingold has been challenged on many levels both legally and in actual campaigning with McCain himself turning down public financing of his campaign and opting instead to raise as much money as possible in order to compete.

The issue is a rather complex one but here are some links that might help.

The Brookings Institute has a Section-By-Section review of the bill.

Open Secrets has an overview.

Of course you can also check out Wikipedia.