How Long Does Google Latitude Keep My Location History?
From http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=163845
Once you enable Location History, it stores your location history for as long as it’s enabled. You may disable Location History at any time to stop storing your locations moving forward. You can also delete your past history entirely, by date range, or by individual location.
But the question really is, does Google actually delete it? With the amount of storage they have my guess is probably not. Your location history is just a grain of sand on their vast beaches.
@Colin,
You are probably correct. : )