Ophiuchus, the 13th Astrological Sign?
Here's the real story.
The ancient Babylonians divided the year into 12 segments, the Babylonians being fond of the number 12 (and also the number 60), and gave names to star groupings that corresponded to each of those twelve segments, enabling them to observe the sky and determine where in the year one was, a very useful skill in a place where the timing of planting is important. The zodiac has exactly twelve equal divisions because that's how it was constructed. It's a human construct, with no natural meaning whatsoever; basically a bookkeeping device. The leading edge of Aries, the first sign of the zodiac, arbitrarily corresponds to the position that the sun is in in the sky on the vernal equinox, the first day of Spring, which is anciently the first day of the year. The key point is that a "sign of the zodiac" is one of twelve equal divisions of the solar year. (These are not to be confused with months, which are anciently defined by the moon's cycle.)
There are, of course, other asterisms in the sky, such as the Great Bear (Ursa Major) and Orion, which are well known to most people but which are not part of the zodiac because they are not in or near to the plane of the ecliptic, the path the sun takes on its apparent annual cycle through the sky. Now let's fast forward to 1922, when the International Astronomical Union (IAU) formally adopted its constellation map, dividing the celestial sphere into 88 named chunks of astronomical real estate. In so doing, they largely kept the traditional Western names for these asterisms (although some of the Southern hemisphere constellations have modern names because those asterisms were not visible to the Babylonians and so they never named them), but the boundaries they settled on did not take into consideration the Babylonian origins of the signs of the zodiac or their astrological significance. As a result of their lack of concern, the ecliptic ended up passing through not twelve constellations (as it would had they remained faithful to their Babylonian predecessors) but indeed thirteen, and the division is not even remotely equal. The thirteenth is Ophiuchus, the Serpentbearer; the ecliptic passes through one corner of the constellation's defined area, although not particularly close to any major star in the constellation. The key point here is that a constellation is one of 88 (unequal) divisions of the celestial sphere.
The thing is, this isn't new. Astrologers and astronomers alike have known about Ophiuchus' intrusion on the zodiac since, presumably, 1922. Some astrologers think this matters; others don't. I've seen complete astrological systems based on the Ophiuchus being part of the zodiac, and I've seen so-called "sidereal" astrologies that take into account precession, which I talk about below. The ones that don't are called "tropical", for some reason I don't recall anymore. Diehard skeptics, of the sort who have a compulsive need to prove astrology wrong, often trot the Ophiuchuan issue forward as "proof" of the wrongness of astrology, along with the precession issue, and it's quite likely that the press release that started all this was motivated by that attitude. Astrology, like all forms of divination, involves the use of essentially randomly-generated symbols to spur self-reflection. The symbols used and their correlations are basically arbitrary; as a result, whether the symbols correspond to anything "real" or not is completely irrelevant. You'll get essentially the same results from astrology using the classical Babylonian/Greco-roman zodiac as you will with using this not-really-new 13-sign approach. Or you can play with Vedic astrology from India if you want something completely different, although the cultural context there may be too foreign for most Westerners to get much from it. Or not. Whatever floats your boat.
In addition, there's an additional complication. The Sun's position on the first day of spring, which originally defined the leading edge of Aries, as I mentioned above, is no longer in Aries. The axis of the Earth's rotation precesses in a cycle of about 26,000 years, causing the apparent position of the Sun against the celestial background to make a full cycle around the sky over that 26,000 year cycle. We're a couple thousand years into the cycle that was started when the leading edge of Aries was defined as the vernal equinox, and as a result the Sun is actually in Pisces on the first day of Spring. In about five hundred years, it'll be in the constellation of Aquarius on the first day of Spring, and according to most astrologers it's already in the sidereal sign of Aquarius, which is the origin of the popular phrase "Age of Aquarius". However, the astrological sign of Aries always starts on the first day of Spring, because that's how it's defined; where the Sun is against the stars in the sky simply isn't part of that definition. The Babylonians almost certainly didn't know about precession of the equinoxes.
Fundamentally the error here is with the Minnesota Planetarium Society, who has unnecessarily (and likely willfully) conflated the astronomical concept of "constellation" with the astrological concept of "sign". A constellation is not a sign, even though there is a historical relationship between two, and in fact twelve of the constellations have the same names as the twelve signs. The IAU did not, in 1922, create a thirteenth sign of the zodiac when it decided to define Ophiuchus to include a bit of the ecliptic. Unless, of course, you decide that you want that to be the case, in which case they did—but only for you.
So if you're a fan of traditional astrology, you can go on using it the way you always have, without worrying about this. It doesn't matter. On the other hand, if you want to worry about it, you can do that too. Just don't lose any sleep over it; that would be foolish indeed. As I mentioned, astrology is an entirely human creation, as are the astronomical names for the asterisms, and these definitions and symbolisms can be changed by humans whenever they want, but only if they want to, and not just because some "skeptic" demands it of them.
Addendum: Apparently AOL's article on this nonsense suggests that the Babylonians deliberately skipped Ophiuchus because "they wanted there to be 12 signs". This claim ignores reality, which is part of the basis of my rant on the Internet being used to spread ignorance. Ophiuchus is certainly near the ecliptic (and there is evidence that Greek and Roman astrologers even read some significance into this, treating the sun's near-passage to a bright star in the asterism as a meaningful event), but the fact remains that the zodiac is defined to have twelve signs in it. The modern fictitious "discovery" of a "thirteenth sign" is merely a consequence of the modern definition of the constellations and has nothing to do with the Babylonians.