I've used Excel and PowerPoint both.
The problems with excel are two-fold. For HST and other triangles, it is hard to color just half of a cell, and if you are printing, the results are not always exactly what you are seeing on the screen. The second problem I got around by embedding the spreadsheet into PowerPoint.
Powerpoint is great, and depending on how precise you are with your mouse, you can draw some great applique designs. By using the "group" function, you can create one block from autoshapes, then copy it through many iterations to see what a whole quilt would look like.