A few tests confirmed this. A test file compressed with gzip came out to 318kb. .zip provided 308kb. bz2 did 189kb. w00t!
I tried rar. 142kb.
Compressing a somewhat-random sample from my hard drive yields 301mb for RAR and 312mb for bz2.
So much for bz2.
. . . actually, I've got a few ideas that might be able to give significantly better compression than the Linux utility. But maybe I'll play with it more later. :P