YES! No builder in my market - Indianapolis and surrounding counties - will increase the price of the home if you have an agent so it doesn't cost you anything. A good buyer's agent can usually negotiate more free items for you than you will be able to negotiate for yourself. Because of their prior experience with a builder they know what things a builder is likely to throw in - closing costs, stainless appliances, etc. Additionally they should be following the deal thru from contract signing to closing so you have someone you trust to answer your questions honestly every step of the way!
I always go with my buyers to every event they have with the builder until closing - contract signing, inspection, final walk-thru to make sure whatever commitments get made to them are followed thru on by the builder.
So again the answer is YES - use a buyer's agent!