There is a blog posting by the developer of Super Duper! that has some interesting details about what happens to compressed files when they are copied by Snow Leopard using different copying engines:

Individual file compression under Snow Leopard is not maintained on the backup

This issue has been fixed with the SuperDuper 2.6.2 Update.

Very interesting and Shirt Pocket Software is to be commended for discovering and, as JChusi pointed out, correcting in the SuperDuper 2.6.2 update.

However, what happens with Carbon Copy Cloner, Time Machine, Silverkeeper, et. al. — even drag and drop copies of compressed files remains an open question. I wonder too about disk space allocation when compressed files are copied to the iDisk. With a 50th anniversary party staring me in the face this Friday, it is safe to say my wife is not going to allow me time to experiment with this, but hopefully someone else will have sufficient intellectual curiosity and time to test using other copy methods.

I look forward to seeing the results of such testing.

Happy 50th, Joe. Please extend my best wishes to the missus.

Some marriages don't last 50 minutes, let alone 50 years. (My 42nd will be in January).

Happy birthday, Joe! My best wishes for another 50!

> Happy birthday, Joe! My best wishes for another 50!

That's anniversary, Alex.

Wow...quite a milestone!

Congrats, both from me and on behalf of all who haven't seen your post.

Thanks, Artie! I really got confused; just thought our Joe is a young guy; in fact he is! Could not even think of a gold anniversary...
Joe, sorry for the confusion and happy, happy anniversary!
I only had a 20th this year...

You might find some of John Siracusa's discussion of compression under Snow Leopard to be of interest (scroll down to Installation footprint).