Small Businesses, Creatives and Freelancers - How Much Do You Share In A Pitch?

This post is one I've been thinking about for a long time and now that some agencies are pushing to retain creative rights to their ideas throughout the process, it's doubly relevant.  I really suggest you read the article in Adage, it's clearly a growing problem. 
When you're a creative team or shop and you make your money by crafting and then executing ideas (designers, social media folks, artists, etc.) it's hard to know how much to give clients in order to show off how great you are and what to keep hidden so that you get the job. 
This is made much more difficult when there are people out there that want you to come up with ideas, pitch them on it, not hire the team, but still own the idea that you came up with for the pitch.  It's not a ton of people, but enough to make creatives a little nervous.
 I sell my ideas and analysis on how a brand should use social media and other new mediums of communication  so new clients always want to see some ideas and I don't blame them.  No one wants to simply "take your word for it" that you know what you're doing.

That said, know that it's ok to decline to provide a complete idea until you are working together.  I am not terribly comfortable coming in the door with a complete idea without having spoken fairly extensively with the client about resources, objectives, team experience, goals, and timeline.  Virtually every prospective client that I explain this to completely understands this and respects that I want to create something that might take some time to craft.  A free idea just might give you what you paid for it.... nothing.
In my opinion,  the pitch process itself is becoming a little outdated given our new mediums to spread messaging.  Back in the day when everything was about TV and print, crafting a great message could be done without as much planning.  An agency or freelancer could come up with a really great message or idea, blast it out on TV, and even develop the product itself around this great idea.  Now, your audience wants to know that your idea is based on making their lives easier and better.  Also, they don't want to hear it on TV, they'd like you to be on their medium of choice. 
It's almost impossible to do all of this on the front end and provide a slam dunk idea without having some serious discussions with your client.
Because ideas are becoming a lot of work to tailor to the needs of our changing consumers, the people who are coming up with them are getting more and more protective.  
To update your pitch process you'll need to explain to your clients that the communication landscape is changing.  They don't have one audience - for example Teens.  You have alternative teens, music loving teens, brainy teens, career oriented teens, rebel teens, and countless other groups that all spend time in different places with different messaging opportunities.  One idea targeting Teens is probably going to flop, or at least waste a lot of money missing the mark.
Show your prospective client how you might target one slice of the Teen audience so they can get an idea of your process and leave the rest until you have a formal contract.