Swine influenza flu or SIV, in the strain currently getting so much news coverage, is descended from or related to a virus endemic to our porcine friends that developed into a zoonosis. The symptoms of swine flu in humans are identical to that of other types of flu: chills, fatigue, et cetera, although an SIV infectee may additionally suffer some diarrhea and vomiting above and beyond average flu symptoms.
Like other zoonoses, you contract swine flu by exposure to infected animals - whether you work with them as a vet or in a slaughterhouse, or if you are some sort of pervert - although it's also fully possible to get the disease through contact with a person who fits one of the above descriptions. The 2009 outbreak contemporary to this writing is, as Don J points out, not necessarily a zoonosis, but related to said type of disease, and began in Mexico, clustered around Ciuda de México, San Luis Potosi, Aguascalientes and Oaxaca. In the US, cases have also occurred in Los Angeles, San Diego, Dallas, the flyover*, and New York, New York. The CDC's website currently says that there have been 40 confirmed cases in the U.S. (update: 64 cases, as of April 28th) and 149 cases worldwide.
If you get swine flu, take the antivirals oseltamivir and zanamivir - unless, of course, the strain continues to evolve and these drugs become ineffective. Don't use antivirals like Tamiflu unless you really need them; this helps create viruses that can outdo the drugs.
One reason you should pay attention to the news about swine flu is that it doesn't seem to be limited, so far, to the already weakened (e.g. the elderly or chronically ill). Kids have gotten it - kids who, as far as I can parse the news, were otherwise hale before contracting SIV. Another reason: Obama almost got it! No joke. I read it in the NYT this morning - he was given a tour of an anthropological museum or somesuch by a docent who later passed away with swine-flu-like symptoms. Damn that man and his paying of visits to neighboring nations. But don't worry, he's probably safe now - symptoms show within 24 to 48 hours of exposure, and it's been longer than that - we saw him playing golf this morning.
One reason not to pay attention: only 149 deaths confirmed worldwide? That's out of six billion. Let's talk about the epidemic of suicide among queer youth or the epidemic of diabetes among people of color or fucking AIDS and homelessness and alcoholism and getting hit by lightning. Life is short; don't follow the Twitter updates about this thing, because you are probably not even going to know anyone who gets it.
*I propose an addendum to Murphy's Law: If something can go wrong, it will - and it'll happen at least once in Flint, Michigan.