Is MSG necessary or what to replace it with? I have always heard that you should stay away MSG. For example when buying bouillon crystals we should always make sure that it doesn't contain MSG. Yet I came across this recipe for spinach soup that calls for 1/2 teaspoon of MSG. This got me wondering are there any pros to MSG. Should we stay away from it or should we incorporate it into our diet and if so should we limit how much we ingest? If it is 'bad' then is there something I can replace it with when a recipe calls for it?
You should refer to the discussion here:
Are MSG and Accent (Seasoning) the same thing?

Some relevant points:
MSG is found naturally in seaweed and other things. It is used to enhance the flavors it is combined with.

It is completely harmless unless you are limiting your sodium intake. Check out the wikipedia article on the subject as a starting point:
http://en.wikipedia.org/wiki/Monosodium_glutamate#Health_concerns

In short there has been no linkage to any adverse effects found in many controlled studies.

As far as replacing it- You can leave it out altogether or add a little salt.