I can only recommend removing the repository rubies and install it via RVM (Ruby Version Manager AFAIK). This will also allow you to have several versions installed, should you ever need that.
bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)
echo "[[ -s "$HOME/.rvm/scripts/rvm" ]] && . "$HOME/.rvm/scripts/rvm" # This loads RVM into a shell session." >> .bashrc
Then RVM should be installed. Close current terminal and reopen, in order to reload the bash profile. Ruby can now easily be installed by typing
rvm install 1.9.2 #Replace with whatever version you'd like (1.8.7, ree etc.)
rvm --default 1.9.2
This will also install rubygems, and the alias commands for you.
Since none of these commands should be sudo'ed, you will not experience permission problems with gems later on either :-)
Edit: To answer the last question, installing "ruby" from apt will install ruby1.8 too. It's even the same version, but with links fixed. You could just do a
sudo ln -s /usr/bin/ruby1.8 /usr/bin/ruby
to fix the links :-)