Major - P3 There is no indication that the insert failed. getLastError should report that creating collections that start with system. isn't allowed.
> mongo
MongoDB shell version: 2.2.0
connecting to: test
test[12:8:21]> show collections
test[12:8:24]> db.system.foobar.insert({a:1})
Inserted 1 record(s) in 0ms
test[12:8:30]> db.system.foobar.find()
Fetched 0 record(s) in 0ms
test[12:8:42]> show collections
test[12:8:46]>