It seems to me that there's no real point in arguing about the significance of the rather large +/- 7 points margin of error on this Newsweek poll showing Barack Obama in the lead for the Iowa caucuses. For something like this, uncertainty about the likely voter screen are probably going to be a bigger problem than sampling error anyway.
But even more to the point, in a close, multi-candidate race the actual method used by the caucuses to allocate delegates starts to make a big different. This method is, especially on the Democratic side, very complicated and tactical voting can start to make a big difference. This is an issue I haven't seem much coverage of, probably because preparations for it on the ground won't start happening until much closer to election day, but one key factor in Iowa is going to be where Edwards and Obama supporters go in caucus sites where they aren't strong enough to win delegates for their guy. Part of what made Howard Dean's task in Iowa so difficult was that almost everyone who wasn't firmly in his camp was firmly against him. In DC, at least, people tend to have Hillary as their first choice or else as a third or lower choice. If that pattern exists in Iowa as well (and I'm not sure that it does) that can be a big problem for her.