just did some tests with 16MB of files of all types...

Winzip -- compressed to 12 MB
WinRAR -- compressed to 6.94 MB
WinACE -- compressed to 8.5 MB
ARJ -- compressed to 10.1 MB
MS CAB -- compressed to 13.1 MB

Winzip did the least compression barring Bill's CAB..
But yet its very popular.. any thoughts?

BTW, were this the same results you got?