Ok, maybe this is a noob question, however...
I needed to install some packets from extra-testing and extra-devel catalogs, so I added them.
I can see that, for many applications, for example macchanger here:
http://maemo.org/packages/view/macchanger/
there are Extra, Extra-testing and Extra-devel versions, all 1.5.0-4.
So, if I have all the catalogs, which version will be installed by default?
To avoid any trouble, I deactivated extra-testing and extra-devel catalogs after installing the packages I needed.

By the way, if for example I want to install a package from terminal which belongs to extra-devel catalog, by I don't have activated that catalog, it won't install, right?
For example, I tried to install John The Ripper with apt-get install john, but it installed only after adding extra-devel catalog.