The topic is interesting, and I wouldn't be surprised if some new type of propulsion technology eventually becomes reality, but what little I've read about this tells my gut that this isn't it.

One doesn't claim violation of Newton's Laws lightly. The sloppiness of the initial conference paper and the (still) lack of peer review are warning signs.

http://arxiv.org/pdf/1101.1063 (10 page .pdf):

Culling Progress

To avoid the extremes of reflexive dismissals and
sensationalist hype common with revolutionary pursuits,
it is recommended to focus on the rigor and objectivity
of the concepts rather than trying to judge their
feasibility. An impartial feasibility assessment on
unfamiliar topics is as difficult as a research task unto
itself. Instead, the level of rigor is easier to judge.

Classic symptoms of non-rigorous work are
reflected in Langmuir “pathological science” [3],
Sagan’s “baloney detector” [4], Baez’s “Crackpot
Index” [5], and the lessons from the NASA
Breakthrough Propulsion Physics Project [1: Ch 22].
Representative symptoms from those sources include:

• Selectively addressing supporting evidence while
neglecting contrary evidence or the possibility of
false-positives.

• The magnitude of effect remains close to the limit
of detectability, along with claims of great
accuracy.

• Drawing conclusions from inadequate sample sizes
(Statistics of small numbers).

• Confusing correlation with causation.

• Lack of relevant reference citations.

Yup. There are warning signs...

Scott writes:

The only test that will truly convince is putting one of these in a cubesat and sending it off to the Moon under thrust. However, I've read comments (unsubstantiated, so hearsay right now) that the inventors of the various drives (4 at last count) were all given the idea from observations of microwave communications satellites whose orbits were decaying faster than expected.

It's a good idea, but I doubt that would be conclusive unless they find a way to get a decent amount of thrust out of them. (E.g. variations in the atomospheric density could swamp the thrust.) And if the satellites are broadcasting microwaves toward the Earth, shouldn't the "thrust" push them to higher orbits? IOW, isn't it backwards if there's some mumbo jumbo physics really happening?

Careful science is really, really hard but it's necessary when one is trying to prove something tiny exists (or doesn't). Some of the Millikan's Oil Drop apparatuses were quite sophisticated in order to try to reduce possible errors. The same principles are used these days in the search for fractional charge:

https://www.slac.stanford.edu/exp/mps/FCS/FCS_hist.htm

It'll be interesting to see if they actually publish anything about the EM Drive... :-)

Cheers,
Scott.