Solar gain and today’s windows

My friend Janice and I were talking a couple of days ago about how materials have affected solar gain. She carefully positioned her house as a passive solar vehicle, yet she does not get solar heat from the position due to the advancement of windows, which seem to insulate from both directions. Although the house is tight, it does not warm up in the sun. What’s up with that?
When buying windows, you quickly realize that the best parts of any glass product are presented by the manufacturer. Low-E! Low-E+! Sun-Gard! Protects from UV rays! In a nutshell, they aren’t telling you what you want to know—that perhaps you won’t warm up as much as you thought you would, or that the bottom of the line is sub par thermally, or that your carpets will/won’t fade.

I don’t know what will happen with our house; the windows are not yet in. We ordered middle-range Andersen 400 Windows with Low-E4 glass (standard). I would love your comments about your experience with combining new window technology and passive solar gain, so let me know.