Say I’ve got an app with a laughably awful GUI setup screen. I could fit 90% of the properties I need to let the user set up with one of those boxes that look like
▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪ ▪height ▪ 1.3in ▪ ▪width ▪ 3.0in ▪ ▪top ▪ 3.2in ▪ ▪left ▪ 2.3in ▪ ▪caption ▪ 'awesome'▪ ▪order ▪ 3rd ▪ ▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪▪
But, are these really good and usable or do I just assume they are because as a programmer I use them all the time in my IDE?
A critical item that makes it much more user friendly is categories. As Oddthinkingnoted in his response, four or five items is about right.
Although, you can get away with more as long as you group them very concisely and carefully. For instance, height and width can and should be grouped together, because whenever users specify one they are used to specify the other.
If your categories are very well laid out and have only four to five items in them, then your setup screen can contain a lot more options without seeming confusing, because the titles tell them what kind of information they need at their disposal before they attempt that section.