It seems that most people are missing the point.
First of all, to the people who question how I have that kind of electrical demand: When the basement is complete I will have a three story home with approx 3000 sq ft, and at least six bedrooms. A home theater, and a photography studio, plus woodworking equipment in the garage - table saw, drill press, planer, band saw etc. For heating/cooling I have three a/c compressors, including a heat pump with a 5kw heating element. Double ovens in the kitchen. One large fridge, large freezer, plus two small fridges. Attic ventilator, dishwasher, electric clothes dryer. These things add up. And the shop equipment wasn't even factored in, because I only use those one at a time on a 20A circuit (no 220v equipment). Nor am I factoring in the home office with several PCs on all the time, with a floor standing 8000BTU A/C unit to keep the room cool.
My current system would handle everything fine, but the addition of the basement changes everything. I really don't understand why they didn't put a 200A in to begin with.
Secondly, to the people who say that I will never have that kind of demand at one time: I freaking know that. That's not the point. The point is, will it pass inspection? What am I going to do if the inspector looks at the size of my home and all the breakers crammed into the box, asks for a load calc, and I say "well it's over 150A but hey I doubt I'll use it all the time"? The worksheet that I used came from a book based on the 2005 NEC, and the formulas take into consideration the fact that you aren't pulling the entire load all the time. The final figure is a minimum, which means my box has to handle it.
As it turns out, I did make one error by not reducing the load from my double ovens to 65%, which changed my total load to 171A. Still higher than 150A but I get a bit more room.
Lastly, I want capacity for future renovations, like a screened in deck. And the extra panel size will avoid a subpanel, which is a good thing because the room with the breaker boxes will be my future office.