Unfortunately, it is generally recommended that you do not compress js or css files, since there are browsers out there that do not support it properly (1). They support compressed text/html content, but sometimes mess up with any other text based content that is compressed.

But using mod_deflate (or mod_gzip for Apache 1.3) is definately something that most admins should be looking at.

(1) http://support.microsoft.com/default.aspx?scid=kb%3Ben-us%3B327286