QUOTE(CherryXS @ Jun 26 2008, 08:42 AM)

For the time prior to your entry to US, just write your last home address in UK--and don't bother writing down the trips.
For time after that point, write down the trips.
Did you read the N-400 Instruction Sheet?
"Part 7. Time Outside the United States (Including Trips to Canada, Mexico and the Caribbean).
A. Write the total number of days you spent outside of the United States (including on military service) during the last five years. Count the days of every trip that lasted 24 hours or longer.
B. Write the number of trips you have taken outside the United States during the last five years. Count every trip that lasted 24 hours or longer.
C. Provide the requested information for every trip that you have taken outside the United States since you became a Lawful Permanent Resident. Begin with your most recent trip."
If you are filing 90 days before your 3rd PR card anniversary, you can only fill that out to the date you filed the application. Go back five years from that date, then count the days you were out of the country until the time you arrived and add that to days in step B putting the total in step A.
Does it make sense? What does make sense? Just do it if you want your citizenship.