Had generated a couple of PDF documents using CutePDF (which, by the way, rocks).
One was a PDF print of a complex one-page Excel sheet, and the other was a PDF print of a simple one-page Firefox page.
I noticed that the simple Firefox print came to some 40 KB whereas the much more complex Excel print came to a mere 29 KB, which seemed wrong.
I didn't fish around inside the PDF code to see why. Instead, I thought I'd fiddle with the (PostScript) print options to see if I could make things better. After playing with a couple of options, I managed to get th Firefox print down from 40 KB to 17 KB, whilst apparently retaining the same image quality.
The thing that made the difference was "TrueType Font Download Option". This appears to be on "Automatic" by default, but I changed it to "Outline" and this change resulted in a smaller PDF file being generated. (This option is buried quite deeply.)
Re-printing the Excel sheet with this setting resulted in a small (2 byte) increase in PDF file size.
That being the case, I've now made that option be the default on my system.