MythBusters also did an episode on this (Season 7 Ep. 22: "Hidden Nasties") (see:
http://en.wikipedia.org/wiki/MythBusters_%282009_season%29#Rat_Pee_Soda). They also concluded that this is just a myth. While it is possible that rats could urinate on the tops of soda cans, they conducted a study using cans they found around San Fransisco, had them analyzed by Stanford, and found that few had any urine on them. Furthermore, the professor at Stanford stated that the deadly pathogens wouldn't be able to survive in dried urine for any real length of time, and would most likely be fully digested in the stomach before it ever entered the bloodstream to cause an infection.
Snopes and Urban Legends also mention that most cans stored in warehouses are in cartons and are usually wrapped in plastic, so even the possibility of a can being contaminated with urine is highly unlikely. So if there is any contamination, it would occur at a person's home, after they have opened up the carton.
I've seen this for quite a while, but was disturbed when I saw this story getting spread around on Facebook... I kept commenting on those posts linking to Snopes to help curb this disinformation. I still don't understand why so many people seem skeptical about what an actual scientist would say, yet readily believe something that gets passed to them on Facebook or some other on-line medium. It's like that State Farm ad where a woman and her neighbor are talking and she claims that there is a law that everything on-line must be true, and she found this out from on the internet!