Joe Calabrese said:
I've been to a few and there are what you put into it. They can be fun, exhilarating and very, very frustrating.
Make sure you check out who will be there and research them to see what projects they do and what they are looking for.
I've participated in a number of them on the other side of the table. I can tell you that it's equally frustrating for the agents, producers, etc because so few of the writers know how to pitch, they let their nerves get the best of them and give a "and then, and then" recitation of their story. I strongly suggest reading up on pitching and practicing your pitch as well - both books Joe mentioned are good resources.
First and foremost pitching is about establishing a relationship and rapport - even in a cattle call environment such as a pitch fest it is possible to do so. And you can have much more success doing so - when you are pitching in person rather than querying via a letter. Of course, in some cases it can have the opposite effect - I've had writers pitch themselves out of a request after hooking me with the logline, by boring me with the details.
As for whether they are worth the money or not, I won't make that call - but I will tell you that every producer, agent and manager I know who particpates - are there because they are hoping to find a project they love and will make a lot of money off of. It doesn't happen often - but then again it doesn't happen often when you query or have your agent submit.
The Screenwriting Expo which is held in LA every fall has a huge pitching event - they also offer pre-pitch coaching sessions.
Hollywood by the Bay holds their Spec Script Marketplace every few months. They also offer pitch coaching before the events. Their next event is in July.
Sherwood Oaks Experimental College also has many different pitch events.
It's sometimes difficult to do research prior to an event - because the participant lists are often not finalized until the time of the event. Often the promoters will list past participants in their event marketing. Most of these events do provide you with a list of attendees and their credits so you can try to target your pitches to some extent.
Most of these events are held in LA - but on occasion they are held elsewhere - there was recently a large event held in New York.
Just getting the opportunity to experience what it's like to pitch is often worth the price of admission.