repl0:PRIMARY> db.bar.find()
{ "_id" : ObjectId("5418c8d2fba52216ba4ca523"), "dt" : ISODate("1970-01-01T00:00:00Z") }

./mongoexport -d foo -c bar -o foo.json
connected to: 127.0.0.1
exported 1 records
cat foo.json 
{ "_id" : { "$oid" : "5418c8d2fba52216ba4ca523" }, "dt" : { "$date" : "1969-12-31T16:00:00.000-0800" } }

./mongoimport -d foo -c bim --file foo.json
connected to: 127.0.0.1
exception:BSON representation of supplied JSON is too large: code BadValue: BadValue: Year out of range:  1969
2014-09-16T16:36:12.215-0700 check 0 0
2014-09-16T16:36:12.215-0700 imported 0 objects
encountered 1 error(s)