It's quite a rare condition (often linked with Kartagener's Syndrome), on the order of less than 1 in 100,000.
Basically, the symptoms are that your organs are reversed. There are various stages, from a few organs to complete reversal. There is nothing life-threatening in having situs inversus, besides the fact that all your X-Rays are backwards. You're not predisposed to anything, besides being left-handed. You can go about living a normal life, putting your pants on the same way as everyone else.
There are differences in a situs inversus patient's body, but most are internal and you wouldn't notice unless you're undergoing surgery. If you have a mild case of situs inversus, perhaps only one or two organs are reversed. Situs Inversus Totalis encompasses the entire body, meaning everything is flipped. My neighbor has the condition, and has to wear a Medic Alert tag, in case she's knocked unconscious and the doctor is listening for the heart on the wrong side.
First, the heart is normally on the left side. In most cases of situs inversus, it's on the right instead. You would need a Medic Alert tag for something important as that. There are other symptoms; in males, the right testicle is lower than the left. The lobes of the brain are switched. Your liver, pancreas, and appendix are all on the opposite side of the body. However, everything symmetrical, like the eyes, ears, and kidneys should still be in perfect shape.
There is a problem with males who have situs inversus totalis; there's a strong chance they're sterile. Sperm are the only cells in the body that possess flagella, a tail to propel the cell. It's made of microtubules composed of proteins, which move the entire tail back and forth. For still partly unexplained reasons, the proteins come out malformed, meaning the sperm can't swim the distance, leading to infertility.
This doesn't mean it's impossible to father kids. First, it doesn't happen to everyone who has the disease. Second, fertility clinics have many methods to help conceive, such as artificial insemination and in-vitro fertilization.
Women who have situs inversus do just fine though.