Using Programmed Fills
This is pretty much what I've figured out so far. As I learn more I'll update this little guide page. If anyone has figured out anything that they think I should include, let me know and I'll add it.
The way you will apply Programmed Fills is the same in Design Center and Layout & Editing.
First, from the "Region Sew Type" drop down menu, select Prog. Fill Stitch.
Now, click on the Sewing Attribute button 
to open the Sewing Attribute dialog box:
You see that you can select whether or not to apply undersewing, select the density
and/or select the stitch direction on the left side of the box. On the right side of the box
you can select and modify programmed fills. Clicking on the "Browse" button
will bring up this dialog box:
On the right side of the box you can scroll through the fills in your
Pattern folder. If you have stored fills in a different folder, you can locate and
select that folder on the left side of the box. Those fills will then appear in the window
on the right side and you can scroll through them to select the one you want.
This is the Programmed Fills stitch attributes dialog window:
The stitch direction (not to be confused with the pattern direction) that you select from the left side of the box has a great deal to do with how the pattern will look when stitched out. This is twirl.pas stitched out at 45º.
:
This is the same pattern stitched at 90º:
You can see how drastically a change of stitch direction can change the appearance
of a pattern. It’s easy to see the reason for this when you view a basic fill pattern.
Stitches set running in the same direction as the stitch direction will NOT stitch.
Look at the pattern below:
In order to get the full effect of the pattern, you know that you do not want to set the stitch direction to 160º, 30º or 90º. This sample was stitched at 90º. Notice that the vertical divisions do not show:
In this sample, however, with the stitches set at 90º, the stitched sample looks just like the pattern:
The reason is that there are no 90º stitches set in the pattern. In fact, 90º runs fairly perpendicular to every stitch in the pattern, giving a very pleasing result.
In addition to stitch direction, you have 3 more variables.
You can choose to offset the rows:
or the columns:
You can also turn the pattern in any direction that you need so that it will complement your design:
.
Once you have selected the fill you want to use you can use it "as is" or you can modify it to fit your design needs and preferences. The default size of the fill pattern is 7.5 mm, or 30% of an inch. You can make this area larger or smaller or you can alter just the width or just the height, elongating of shortening the pattern.
Here are some variations in row and column offsets, pattern size and pattern direction with Heart2.pas:
stitch direction 90º, all other settings default
stitch direction 90º, column offset 50%
stitch direction 90º, row offset 50%
stitch direction 45º, column offset 50%, width reduced to .25", pattern direction 315º
Since this pattern seems to stitch out best with a stitch direction of 90º, the stitch direction needed to be altered accordingly when the pattern was rotated.
In Design Center you apply the programmed fill with the attributes that you've selected by clicking on the area you want to fill while the Sewing Attribute Settings window is still open.
In Layout & Editing you apply the programmed fill with the attributes that you've selected by clicking on the "apply" button.