There were 3 suits filed the day after the ballots were counted (only because the courts said it wouldn't hear any cases against Prop 8 until AFTER the count) claiming that the ballot initiative shouldn't even have been on the ballot. Had it lost, there would have been no reason for the court hearings. Since it passed, 3 suits were chosen from dozens actually to be hear by the Supreme Court of CA questioning the validity of the Proposition.
The main argument is how the vast is the language of Prop 8 and what is to become of those that were married from May to Nov 2008. The notion is that since the first Amendment in the CA constitution guarantees freedom and liberty for all residents of CA that making a revision to exclude a group of people from a right that was deemed a fundimental right should not have been up for popular vote. Instead the Prop should have been put up to legislation for 2/3 vote before it was put on the ballot.
Both sides are going to be making their arguments today and the courts will have up to 90 days to decide. I have heard, however, that the courts have already drafted a decision even before hearing the case. This is normal as they have already made a ruling on this stuff, the May ruling that started all of this.
The language used in the ruling in May was very clear, very widespread, and very powerful about the rights of all of the people and I am sure this will be revisited and be a major influence to the decision from the courts about this.