Not if you apt-pin them and only take what you need. I
never had a
problem with that in the last years from woody to wheezy.
certainly if you are careful and only take what you want from
debian-multimedia.org, and keep track of what is breaking things, then you can
make it work.
I personally prefer to have a separate system for those codecs and such, and use
them as little as possible.
There is another reason to use two boots - Ralf mentioned using wine, and having
a 64bit system. Wine is much easier on 32bit systems, and it would be a good
idea to have a 32bit system (set up to be used via chroot perhaps) for wine
so it may as well be something like Mint which includes the stuff that debian
won't include.
Simon.