Mongo has never supported dates prior to the Unix epoch (Midnight Jan 1, 1970 UTC), but recently support for this was committed to trunk.  It has been a long outstanding ticket that has generated a lot of interest in jira.

I decided to give it a simple trial run for fun so I cloned and built a copy of trunk and fired it up.

MongoDB shell version: 1.9.1-pre-
connecting to:
>{dob:new Date(1900,6,18)})
>{dob:new Date(1950,6,18)})
>{dob:new Date(2000,6,18)})
> db.date_test.find({},{_id:0}).sort({dob:-1})
{ "dob" : ISODate("2000-07-18T04:00:00Z") }
{ "dob" : ISODate("1950-07-18T04:00:00Z") }
{ "dob" : ISODate("1900-07-18T04:00:00Z") }

I’m looking forward to seeing this in MongoDB 2.0.