How portable are NSF grants between institutions and internationally? I'm a fixed-term lecturer (2016-17 academic year) on the job market. I'm hoping to apply for an NSF grant this winter to fund new research. Very hypothetically, if I am awarded the grant, how portable are NSF grants between institutions and internationally? Or if I got both the grant and a job (particularly outside the US), would the protocol be to defer the start of the appointment? Are there obstacles I should know about that aren't listed on the NSF FAQ page?
I just participated in a NASA grant-writing workshop. This question came up there, too. The following rules apply for both NASA grants and for NSF grants. (I'm sure there are differences, but at least what I'm writing is the same for both.) 

Can the grant be transferred from one institution to another?

Yes. 

Check out AAG II.B.h which describes NSF's grant policy:


  
  Contracting or Transferring the Project Effort (Subawards)
  
  
  a.    Excluding the procurement of items such as commercially available
  supplies, materials, equipment or general support services allowable
  under the grant, no significant part of the research or substantive
  effort under an NSF grant may be contracted or otherwise transferred
  to another organization without prior NSF authorization. The intent to
  enter into such arrangements should be disclosed in the proposal
  submission.
  
  b.    If it becomes necessary to contract or otherwise transfer a
  significant part of the research or substantive effort after a grant
  has been made, the grantee shall submit, at a minimum:
  
  (i)   a clear description of the work to be performed;
  
  (ii)  the basis for selection of the subawardee (except for
  collaborative/joint arrangements5); and
  
  (iii) a separate budget for each subaward.
  
  The request must be submitted electronically, and NSF authorization
  will be indicated by an amendment to the grant signed by the Grants
  and Agreements Officer. The NSF grant conditions will identify which
  articles flow-down to subawardees.
  
  c.    Procurements under NSF grants are also subject to AAG Chapter V.C
  and OMB Circular A-110 Sections .41 through .48. (2 CFR §215.41-48)


The grant is awarded to your institution, not to you. Because of this, your institution would choose to do one of the following:


Nominate somebody (e.g. a Co-I) to take over when you leave
Terminate the grant outright
Initiate the grant transfer process (if certain criteria are met, and both institutions agree...)


According to the NASA VIP leading the workshop, transfers between US institutions happen, though they are rare. Either way, if you plan to do this, you should contact all involved parties: your current institution, the destination institution, and your program officer/manager (your designated NSF/NASA contact person) for the grant. 

Can it be transferred to an international institution?

No. 

As indicated in 3.c above, AAG Chapter V.C.1.i indicates that funds can be sent under the following condition (among others): 


  (i)   grantee is not an individual or a foreign institution;


Since both NASA and the NSF are government organizations, they are prohibited from funding foreign institutions. 

There are additional rules for certain countries, at least for NASA: if applying for a NASA grant, you can't have any affiliations with a Chinese institution via the Wolf Act.