Rh77,
Congrats on your house! Did you have any input during the build? If so, what were your upgrades?
In general, builders want to do the minimum required (code) unless otherwise specified, especially on the energy / air quality side.
One more thing about home sealing: The house / foundation interface. In my house while in process of finishing my basement, I got up there to take a look. BIG gaps. I vacuumed and sealed this interface w/ GreatStuff. The basement temp went up 7 degrees! A 1/8 of an inch gap in a 1000 ft sq basement is the same as 1.31 sq foot hole!!!! This solution worked, but during the latest remodel, I had the polyurethane foam installer just back fill these areas, because there were more leaks than I could find, and this was a cheap solution given he was already here, and how much a pain in the ass it is to work there.
ON HVAC: the installer wants things to go in quick, so the compromise is air leaks in the system. This may seem like not such a big deal, but it is. As I said, an built to code home will have about 30-50% of the air leak out of the ducts. Half of the air not arriving or coming from its intended location, so some areas get too much (heat or cold) and other areas don't get enough. This is especially true on the joist covered return ducts. They are usually horrible: Big gaps, wire penetrations and just missing material. The supply and return ducts need to be sealed at every junction. This is easy in a ranch, not so much in other styles. Still, you should do this wherever you have access.
On solar gain: If you are more concerned about cooling than heating, or you live in a climate that is cloudy all winter, like here in south east MI, window films on your south and especially west facing windows are an option. They are cheap and effective, DIY solution. Google Solar Window Films.
This is available at home depot:
Gila Film Products : Residential Window Film - for your Home and Office - Reduce Heat Glare and Fading while Lowering Energy Costs
a better product:
3M™ Residential Window Films