Look for websites that review a particular builder. There, you can read about the downsides. Yesterday's WSJ had a good article hidden in the back pages about builders' selling schemes.
One thing I have noticed is that builders' incentives are usually tied to using the builders' financing (they own the mortgage co.). I thought this was illegal, but what do I know? This reminds me of the financing scams of auto dealers, but they are relatively easy to work with.
Out here, many realtors invested in preconstruction buying, until the downturn left their units unsold. So I would look to a preconstruction realtor-investor for some advice about their experiences. To do this, look for an empty unit owned by a realtor, and talk to them.