About toDate(), why the "15:00:00"?

About toDate(), why the "15:00:00"?

I've put a Formula field which converts a time (which holds date and time like "May 5, 2011 18:08:01") to a date ("May5,2011"). I used "Deadline.toDate()" to achieve so, but it always gives a time like "May 5, 2011 15:00:00". 

Why the "15:00:00"? Shouldn't it be just "May 5, 2011"? 

Please help. Thanks very much!