This affects double-quotes, literal carriage returns and newlines, etc.

% mongo
MongoDB shell version: 1.6.0
connecting to: test
> db.foo.insert(

{x:"foo \"foo\" foo"}

)
> db.foo.find()

{ "_id" : ObjectId("4c659a8dfe7acb2308816965"), "x" : "foo \"foo\" foo" }

% mongodump -d test -c foo
connected to: 127.0.0.1
DATABASE: test to dump/test
test.foo to dump/test/foo.bson
1 objects

% bsondump dump/test/foo.bson
connected to: 127.0.0.1

{ _id: ObjectId('4c659a8dfe7acb2308816965'), x: "foo "foo" foo" }

Fri Aug 13 12:19:04 1 objects found