Answer to your question and method for figuring out other "how to do something ubuntu in debian" questions. A great way to answer a lot of these questions is simply use `apt-cache search` however this is not always enough. The next thing to try is apt-file. Install apt-file:

  # apt-get -y install apt-file

Update apt-file db (might do this on install, I forget):

  # apt-file update

Now the bit you are interested in: How do you add PPAs in ubuntu? Answer: `add-apt-repository`

Does debian have something named add-apt-repository?

  # apt-file search add-apt-repository
  software-properties-common: /usr/bin/add-apt-repository
  software-properties-common: /usr/share/man/man1/add-apt-repository.1.gz

That looks familiar.

  # apt-get install -y software-properties-common 
  # add-apt-repository ppa:libreoffice/ppa

As a long time debian fanboy I have to say "new software is exclusively published on Ubuntu" was kind of funny. Unless you were talking about `upstart` ;) A great reseource for debian is the Debian Administrators Handbook. The section on pinning is:

http://debian-handbook.info/browse/stable/sect.apt-get.html#...

Please look at backports before thinking about apt pinning. Mixing stable with newer releases can sometimes get tricky, while backports are actually designed to work with the stable release.

I've been using Debian stable on desktops for years now with few problems, and backports have only improved in the past couple of years.