This is what I got applying the above procedure to one of my machines.
Before the treatment, df reported I used 398,798 1024--blocks:
df reported 244,668 used blocks;
upx on /usr/bin,
/usr/X11R6/bin, /usr/lib/texmf/bin/i586-linux,
and /usr/lib/gcc-lib/i386-linux/2.7.2.1. 226,270 used blocks;
To sum up, I started with 398,798 blocks and finished with 198,745. Think of
the stuff you can shove in those 200,000 spared blocks! I would have saved
even more if I had used bzip2 instead of gzip.
On average, if you are careful from the beginning and install only the necessary applications, compressing executables and documents will save you some 20 Mb. On a notebook, this can be a lifesaver.