[mathias_10gen]

Locking in particular has improved substantially since 1.6. For example, 2.0 introduced yielding in some cases where MongoDB would go to disk rather than page-faulting with the lock held[1]. This has been extended and improved for 2.2, along with increasing the granularity of the lock from process-wide to per-db. There are plans to increase the granularity further in future releases.

[1] To see an example of the difference this makes see http://blog.pythonisito.com/2011/12/mongodbs-write-lock.html