UPX - Saint or sinner?

Back when I used to code in QB I would use UPX (ultimate packer for executables - available at http://upx.sourceforge.net/) and it would greatly reduce filesize for my executable code. I'm not 100% sure how it actually does it, but I would assume it searches for duplicate code and reassigns how the code is used or something...

...anyway, I thought I would (1) let people who don't know about it find out about this great program and (2) find out if anyone here has good or bad things to say about it. I have in the past used UPX to pack VB programs and it achieves comparable compression to when I used it in QB.

There's one downside I remember, and that's that you can't ZIP or RAR the file to achieve further compression, and usually ZIP/RAR actually achieves better compression than UPX does...it's not good for distributing but it is good for storing :-)

If you know of any reasons why UPX would be a bad idea, please post...as far as I am aware, for small-time programs written for personal use, UPX is an excellent program but I can't be so sure about corporate/professional use of a program like this :-)

Anyway, I added a poll to this too...please vote.

Honestly with todays huge hard-drives I really don't care if the exe is 100K or 10 MBytes, it's the same to me...

It's only one exe (for one application), it's not like MP3s, where you have hundrets...

I think the UPX compresses the exe, and then encapsulates that exe in it's own exe (or something like that), when you run the exe, it un-zips, and runs the un-zipped exe, then closes itself. That explains why you can't use rar or zip to compress it further, because internally it's already zipped...

It's weird that I am in the minority here...I'd have thought many people used this program :-)

Although I admit that most people who use this sort of program are hackers trying to hide their trojaned file by packing it into one file stream :-)