noobie question

What are extension tubes for? After reading many forum postings, I am still a bit confused. Most people talk about them when referencing macro photography, so do they shorten the minimum focusing distance of the lens they are attached to? I would like to get a bit closer with my EF-S 17-85, would extension tubes help with this? thanks a lot!

extension tubes make your lens focus much closer; you can go really close to objects.
but it kinda "forces" you to shoot close, with a tube you cant shoot "normally" :P

and i think some extension tubes dont work with EF-S lenses...

Yes they will help. They are simply tubes with no glass that essentially give the lens more "length". I like to think of it like those dinner tables that spread apart so an extension piece can be put in the center to make the table larger.
I use mine on my 50 1.8 and my 100 macro. You will lose focus to infinity but again it is meant more increasing the magnification of your subject up close.
I know some on the macro forum can give you the equation to work out your magnification with different ext. tube widths and your lens focal length. But the quick and dirty is it will get you closer when working at your minimum focus distance.