My wife and I almost did the flat Lighthouse Century today. We started the metric and continued to the century turnaround for about 90 miles total. Age totalizer exceeds 120 so we're not interested in 15% grades so the "flat" option suits us. This is a beautiful ride - ocean, cows, zebras, rocks, harbor seals and rolling hills; max grade I saw was 6-7%. Most of you who live in the west will have been familiar with this ride as I'm sure it's been around for a long time, but we've only been riding for a year, tandem for about 5 months. Our goal is to be able to do normal California centuries next year which will have 5K+ of climbing I would think. Time will tell.
We hadn't preregistered so it took about two days of checking the buy/sell page every 15-30 minutes to buy two entries. All and all not too bad.
Oh, and I had to do the ride in a pair of my wife's bicycling shorts as mine disappeared enroute. I'm 6' 205 and wife wears a woman's small short. Ain't lycra wonderful.