Here is how you can squeeze out few more kilobytes from your zip or gz files by using advzip or advdef from AdvanceCOMP package (installable from Ubuntu respository) :
advpng -z4 example.zip
mypapit:$ advzip -z4 example.zip
761604 655677 86% example.zip
761604 655677 86%
Saves you almost 6KB per file.
Similarly gzip files can be recompressed the same way to save more space.
advdef -z4 *.gz
mypapit:$ advdef -z4 *.gz
214451 207312 96% coolplayer.tar.gz
21523 20800 96% phex-pkg1.00.tar.gz
26527 25516 96% png2ico-src-2002-12-08.tar.gz
262501 253628 96%
Saves you almost 11KB total.
The differences may be small for most of you, but it means a lot in situation where space is at premium and every little bit of Kilobytes count.
p/s: w00t, this is the first post for 2008!