Should I lock in to today's mortgage rate or wait two days (which is when I'm meeting with my mortgage broker)

I am currently being offered 5.75 with 0 points/0 points origination fee. Should I lock in today (3/18/08) or wait until my scheduled meeting, which is in two days (3/20/08) because the rates will have gone lower by then? Any ideas? Sources would be great. Thanks! Forgot to mention…This is regarding a 30-year fixed loan. http://bit.ly/qyZkw5