Booking in advance does have its' advantages. We booked well in advance for our January 2004 cruise on the Sea, and it was nicely paid for in advance, in addition to being very inexpensive.
Our cruise on the Sun in June (note 2 cruises in one year) was much less planned, and was actually substituted for a talked about Hawaiian land vacation after my daughter graduated from high school. Unfortunately, my budget is having a hard time recovering from 2 cruises in 1 year, especially as the 2nd one was for 4 of us.
Oh well. Time to start saving for the next one, but with 2 kids in college, it may be 2-3 years out.