Syzygy - 10:51 am on Feb 24, 2010 (gmt 0)
As stated, such a thing only goes to prove possession of the work at that given point. It does not prove who created it. Such evidence may be sufficient for a court in some instances, but not in others. Bottom line; there is no harm in it.
Like a lucky charm worn around the neck, maybe it will do you some good, maybe it won't. Just don't rely on it.