Linux Web Magazine, Repositories, Ubuntu themes

I was looking for a free linux magazine, and found full circle Linux magazine. So far they published 39 magazines, and I want to definitely try the magazine, as it seems like they have a consistency.

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I got familiar with the concept of the repository with iPhone jailbreaking. It is basically register a pool (server) to your host, so that it can find and install applications from it. So after I installed Ubuntu, I wanted to register decent repositories. I googled a little bit, and it seemed like getdeb.net and medibuntu repositories are quite important.

For getdeb, quote:
Go to System-Administration-Software Sources, Third-Party Software tab, Add:
deb http://archive.getdeb.net/ubuntu lucid-getdeb apps Add the repository GPG key, open a terminal window and type:
wget -q -O- http://archive.getdeb.net/getdeb-archive.key | sudo apt-key add -

and for medibuntu, add

deb http://mirrors.ucr.ac.cr/medibuntu/ lucid free non-free
deb-src http://mirrors.ucr.ac.cr/medibuntu/ lucid free non-free
I'm not sure if I need deb-src repo, so i didn't install it. There's one more thing to do before finish, type on Terminal to authentificate the medibuntu repo (from Ubuntu Geek):
sudo apt-get --yes -q --allow-unauthenticated install medibuntu-keyring

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For themes, check Bisigi project.
add repository: sudo add-apt-repository ppa:bisigi && sudo aptitude update
install: sudo aptitude install bisigi-themes
Or, install each theme separately. 

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I read aptitude is better than apt-get, as it checks out dependency of the application, and remember it, but I still find a lot of people use apt-get and want to know why. Also I wonder the exact happenings during the installation, and its meaning. As soon as I understand them, i will post it here.