At HEAD, connecting to a config server instance directly, doing an insert to the admin DB, and calling GLE with a numeric w values causes GLE to timeout:

> use admin;
> db.foo.insert({a:1});db.getLastError(3,5000);
Inserted 1 record(s) in 0ms
timeout

The behavior is the same if you connect through mongos and write to the admin DB.

In 2.2 this would just return with the message "norepl"