When Polls are Polls apart

As we get closer to the US Election there seems to be polls coming out from everywhere. What is surprising is that in this day and age, that there can be such as large diference in the two. This morning, one poll has Obama 12 points ahead, while another had the lead at only 6. Without knowing the measures or samples used it is hard to draw an accurate comparison however the expectation would be that they would both be looking at similar samples so the results should be the same…market research, love it, hate it?