What are evaluation criteria for NSF postdoctoral fellowships? I am currently working on applying for an NSF postdoctoral fellowship and I was wondering if anyone had insight into the following questions:


Is it practical to have a proposed research project that is not directly in line with the applicant's previous research (I'm thinking of a research project that in some way falls within the same subspeciality but none of the work I've done before naturally segues into this work)
Is it disadvantageous to apply to work under someone who already has numerous postdocs (say around 4)? The worry would be that a panel would think that this would reduce the sponsor's ability to be an involved mentor
When it comes to Broader impacts, in particular things like educational outreach, is it all right if this occurs in another country if I am applying to be supported by the NSF while at a foreign institution.
I think this depends to a large degree on how intelligently you can write about this subject.  If you have a carefully thought out research plan, and can point to how your previous experience prepared you for it, I don't think it should be a huge problem.  That said, there's no reason to really go out on a limb in the description.  It's not like you're required to do the research you propose, so I would be more inclined to suggest doing a mix of problems from the new and old areas.  Also, talk to your recommenders about it.  If they're enthusiastic, it will really help.
I wouldn't over think this stuff.  It's just impossible to know what people will think.  I would concentrate more on what you think is best for you.  
You should discuss anything cool you've done with educational outreach.  If it was in another country, I don't think it's a problem at all.