If I use jquery or other open source libraries such as Box2D in my App, Do I need to declare that I have thirdparty content when I submit the app? Or is the third party declaration strictly for content from a 3rdparty vendor with whom I have some kind of contract?
Also, Is there any guidelines on attribution obligations: will the PlayBook have a common place to add all the attributions or is it the responsibility of each app to add these within their own app?
Also App World does not list the license of each app. Is that a problem from compliance for apps using OSS components? Or is it expected to be added by the user under the Descriptions?
I am no lawyer..Just making sure I do the right thing for the Webworks app as none of them are approved and I am not sure if I missed something or am I just thinking too much 
Disclaimer: likely no one posting in this thread is a lawyer, me included.
I don't know off-hand whether "third-party content" refers to assets that are visible to a user, such as images, video, audio. It may be defined narrowly or broadly... not sure which.
If it is defined broadly enough to cover source code and libraries, then it certainly would also cover any item for which you do not own the copyright. (Or, more probably, anything for which someone else owns the copyright... by defining it that way I'd say that for public domain stuff you don't need to mention it.)
I don't recall any OSS licenses which say that you must show the license in any place where the work that uses it (e.g. your app) is even listed. That would probably be a bit insane really. So there's no reason I can see why App World should list such things.
I would say it's definitely required, if the license requires a particular mention, such as in the documentation, that you include it there. That may be an About box, or conceivably a link to your own web site where you list additional information about the app. Many OSS licenses, as I recall, say that the license must be included in any distribution, which would include your app, so just putting it on your web site would technically not be good enough. I think you should review and understand each license for included libraries well enough that you can decide that for yourself, or consult a lawyer.
And I don't think you're thinking too much... these license represent specific legal (contractual) obligations, whether or not you have an explicit contract with someone. They are the only reason you are allowed to use those packages, and if you don't follow the license terms you lose the privilege of using them, and may subject yourself to legal action.
