use MongoPerfTest.java to reproduce

antoine@agAntec:~/tengen/support$ java -cp "mongo_2-6-5.jar:." MongoPerfTest
insert: 17945ms
find: 4804ms
antoine@agAntec:~/tengen/support$ java -cp "mongo_2-7-0.jar:." MongoPerfTest
insert: 18852ms
find: 6587ms

inserts are marginally slower (about 5%) but queries are 37.5% slower.
It seems to have introduced by following commit:

commit 66c54120c56f9329b392264ec5efba0b2a292217
Author: Brendan W. McAdams <brendan@10gen.com>
Date: Fri Aug 19 16:05:22 2011 -0400

JAVA-421 - LazyBSONObject exhibits certain behavioral breakages

• Fully functioning implemented LazyBSONObject, fixed string decodes
• Test class now validates all known decodable types for correctness
• Now works correctly, fixes known issues.
• For performance, sanity and memory usage replaced all arraycopy calls
  with ByteBuffer usage which should help overall longterm behavior