That poll is done by Gravis, that only does automated polling. They were off by a significant amount in the 2012 election final polls, so their track record is not good...
Not really. For all of their final week state polls except one, and for the national poll, they were within 3 points or less of the actual final results, which is as good as any of the other houses. The only one they missed significantly was New Hampshire, which they missed by 5 points.
They *do* tend to have a systematic rightward bias, it is true. But one would think Carson supporters (at least) would interpret that as favouring their candidate in the current polls...