1. My cat that is FIV negative will get FIV from sharing a common living area (food/water/litter).
Not true! FIV will transfer from one cat to another from vicious bite wounds - something that is very uncommon for domesticated indoor cats, especially if all are spayed/neutered at the appropriate time. To ease your mind, it is always a plus to adopt two kittens that are FIV+!
2. My FIV+ cat will live a much shorter life.
Cats with FIV can live just as long as a cat without FIV. While they can get sick easier, they are immunocompromised after all, if your cat is kept strictly indoors, kept on a nutritional diet and maintains its routined vet visits, there is no reason why your cat should get sick for no reason! These are all things that you should be doing for your cat anyway - with or without FIV! If they should become ill, they are generally treated earlier, longer, and more aggressively than non-immunocompromised cats (meaning they need to see the vet at the very first sign of illness and may be on a stronger medication or on medication for a longer period of time).
3. I need to worry that I or my dog (or other pet) will get sick.
WRONG! FIV has 'feline' in the name for a reason - it can only be transferred from cat to cat.
4. My cat being FIV+ means that it has AIDS.
Most cats with FIV are actually very healthy; they simply have a virus that is very slowly affecting their immune system, but which can take several years before it has any noticeable effect at all. Most FIV+ cats never even get AIDS; they live good lives and die naturally from all the usual causes of death that any cat may suffer, including old age!
Sources:
Common Myths About FIV
Adopt an FIV Cat!
Feline Immunodeficiency Virus