I am fairly new to the site and to baking bread, just started with both the site and bread at the beginning of the year.  I have been reading volumes of information on starters:  how to make, how to feed, etc.  Isn't a sourdough starter just another form of leavening?  Is it not a wild yeast vs. a commercial yeast?  And if that is the case, can I just substitute a portion of a starter into a recipe that normally uses a poolish as the poolish and drop the commercial yeast and get the same or similar results? 

I was always been put off of sourdough bread because of, well, the sourness.  Now after reading so much information am I right to say that the bread that I could bake with a starter will not necessarily be sour?  Will the starter just be a flavor enhancer and/or a leavening agent?

Theresa