Here's a link I found about Baccillus Cereus, which thrives in starchy foods that aren't kept cold..
or hot enough.
For instance, if a potato salad is put together while the potatoes are still lukewarm, then sealed in plastic and refrigerated, it may stay tepid way too long in the refrigerator. All those added raw ingredients that our hands touched might contain the bacteria, which can multiply in the tepid conditions.
Then when the guests get sick, we blame the mayonnaise.
According to the "four hour rule" I learned in a food safety course, as long as the potato salad is cooled down quickly enough, (uncovered, and perhaps spread out on a tray, so it gets below 41*F in four hours), and kept below 41*F until serving time, there is not much risk. It can sit on a buffet for up to four hours, though a shorter period is better, and setting it into another tray of ice wouldn't hurt.
Here's the exerpt on this particular pathogen:
BACILLUS CEREUS
B. cereus can cause two types of illnesses; the diarrheal type and the vomiting type.
Sources: A wide variety of foods including meats, milk, vegetables and fish have been associated with the diarrheal-type food poisoning. The vomiting-type outbreaks have generally been associated with rice products; however, other starchy foods such as potato, pasta and cheese products have also been implicated. Food mixtures such as sauces, puddings, soups, casseroles, pastries and salads have frequently been incriminated in food poisoning outbreaks.
Symptoms: The diarrheal illness results in diarrhea and abdominal cramps occurring within six to 15 hours of eating contaminated food, and may last up to 24 hours. The vomiting-type illness results in nausea and vomiting within three to six hours of eating contaminated food and also lasts about 24 hours.
Prevention: Keep hot foods hot (above 140 °F) or refrigerate them rapidly if they will not be served immediately. Keep cold foods cold (40 °F or below).
http://hgic.clemson.edu/factsheets/HGIC3740.htm