Definitely. The format is built around people assembling into teams; not everyone will have an idea or attract a team to their idea, so being a part of a team is the majority experience.
It's worth attending just to join a team and get experience with customer development, project management, and just the general process of starting and validating a startup. The networking and coaching are also valuable benefits of the weekend.
Disclaimer: I'm a community leader for UP Global, which means I also organise and facilitate Startup Weekends.
At events I facilitate, approximately 50% of attendees will pitch an idea. This is higher than average because I really push people to be brave.
Those who don't pitch, or pitch but are not selected as favourite by the crowd, join teams around someone else's idea.
As @rbwhitaker points out, working on an idea that wasn't yours can be seen as a better learning experience, because you're not as emotionally attached and will be more flexible. Of course the down side is that you don't get the benefits of input to your own idea.
In either case - go, it'll be a great experience and good networking. Remember to have fun :)
Jay's answer is great, and I completely agree. I just wanted to add one more thing.
Taking an idea through something like Startup Weekend attaches strings to it. You suddenly have a other people who have spent time on it, and may then feel entitled to continue working on it and to get an equal share of the equity.
That's not a bad thing, or rather, that's not all bad. Ultimately, getting others to work on your idea with you is a good thing. But it does present an opportunity for things to get more complicated.
By going and participating, without bringing your own idea in at first, gives you an idea on whether it's the right venue to introduce your idea to others or not.
So I'd actually suggest it might be better to go your first time with the intent of working on somebody else's idea instead of your own. Even working on somebody else's idea, you'll still get all of the benefits that Jay listed.
After doing it once, you'll know better if it's the right venue to kickstart your own idea, and you'll know better how to pitch your idea to get the best results.