The protest can't be the goal in and of itself, rather, it's a tool in a broader toolbox.
In this case, these protests have served as a wakeup call to equality-minded people all over the country. It is an empowering act. But rather than people feeling they've done their part by marching for a few hours, I'm willing to bet that, just like here in California, the seeds were planted for further organizing all over the country. There is nothing more dangerous for the status quo (the "system") than people suddenly feeling empowered.
Kos does a good job of putting the protests in context. I generally agree with his assessment, but I'm not quite as optimistic as he is about the future. What Prop 8 and the protests have done is given us a moment of opportunity.
Too often in the past, though, I've seen these moments slip through our fingers. As Kos also argues, protest fails if it becomes an end in itself. Activist energy is sucked into the task of getting people onto the street and diverted away from doing the day-to-day political work needed to create real change.
We have to follow up our marches with organizing, and we need to look at models that work like MoveOn.org (although I don't think it is as effective as it could be), other campaigns and what may be the best model of all, Barack Obama's campaign. What Obama did was translate enthusiasm into action. That's what we need to do now.