To refrigerate or not to refrigerate- that is the question

Is mayonnaise the real culprit in a picnic food poisoning?  Turns out that is probably not the case - it is most likely the food handling of the other ingredients that was the real reason.
Lee from the Chemist's Kitchen lays out the reasons that some old adages are incorrect:

• Commercial mayonnaise is made in sterile conditions so the mayo itself is not a problem.
• Mayo has a low water content and a high acid content so it is not an ideal environment for bacteria.  
• The main problems with the picnic/potluck potato/chicken salad is the the handling of the other ingredients - the potatoes, the chicken, etc. if left out too long prior to making the salad can begin to go bad or not washing raw vegetables well enough. 
• Also personal hygiene is often a source of bacteria - improper hand washing or a dirty cutting surface can introduce germs.

Typical ingredients in mayonnaise:

Homemade:   egg, oil, spices, vinegar and/or lemon juice
A great simple recipe here: making mayonnaise with a stick blender
Commercial:
Hellman's mayonnaise contains
CANOLA OIL, WATER, LIQUID WHOLE EGG, VINEGAR, SALT, LIQUID YOLK, SUGAR, SPICES, CONCENTRATED LEMON JUICE AND CALCIUM DISODIUM EDTA.
The commercial version will use pasteurized eggs so that they are sterilized and will also be made in a sterile environment.

The main preservatives in mayo are the vinegar and the lemon juice and, in the case of the commercial stuff, the calcium disodium EDTA (see below for more info on this chemical as an additive).

Here is an extended excerpt from Harold Mcgee's book, The Curious Cook (1990) with more info that you really need to know on Mayonnaise!
He also has a long section on mayonnaise in his book, On Food and Cooking.
Turns out you should be able to make about 23 litres of mayo using one egg yolk if done properly!!

Maria's Curry Mayo Dressing

My sister-in-law introduced me to her delicious dressing/dip/sauce!

Mix mayonnaise, curry powder (or curry paste), lemon or lime juice, and salt and pepper in a bowl.
All amounts are to your desired taste and texture.

Use it:

• on cooked vegetables such as green beans or cauliflower
• as a dip with rice crackers or french fries (or sweet potato fries - Yumm!)
• in a thinner runnier form  of caesar salad dressing

This a a great substitute for a cream sauce, sour cream or cream cheese in these situations.  You can substitute almost any other flavours as well!

Extra info:
calcium disodium EDTA
FDA regulations as a food additive:
Calcium disodium ethylenediamine-tetraacetate [(calcium ethylenedinitrilo) tetraacetate]; calcium disodium EDTA - AF, REG, 25 ppm - Fermented malt beverages - 172.120; Antigushing agent; MISC, 60 ppm - Spice extractives in soluble carriers; Color & flavor; 100 ppm - Pecan pie filling, promote color retention; 340 ppm - Clams (cooked-canned), promote color retention; 800 ppm - Dry Pinto beans, promote color retention; 310 ppm - Promote color retention in dried lima beans (cooked, canned); 275 ppm -Crabmeat (cooked- canned), retard struvite formation, promote color retention; 250 ppm - Shrimp (cooked-canned), retard struvite formation, promote color retention; 33 ppm -Promote flavor in carbonated soft drinks; 110 ppm - Promote color retention in canned white potatoes; 200 ppm - Mushrooms (cooked, canned); 220 ppm - In pickled cucumbers or pickled cabbage; To promote color, flavor & texture retention; 100 ppm - Promote color retention in artificially colored lemon-flavored and orange-flavored spreads; 100 ppm - Potato salad, preservative; 75 ppm alone or comb with disodium EDTA - French dressing, mayonnaise, and salad dressing; non-standardized dressings and sauces, preservative; 100 ppm alone or comb /w disodium EDTA - Sandwich spread, preservative; 200 ppm by wt of egg yolk portion - Egg product that is hard-cooked & consists, in a cylindrical shape, of egg white w/an inner core of egg yolk, preservative; 25 ppm - In distilled alcoholic beverages - 172.120, promote stability of color, flavor and or product clarity; PRES, REG/MIA, 75 ppm - Oleomargarine - Part 166; 365 ppm - Promote color retention in legumes (all cooked canned, other than dried lima beans, pink beans and red beans) - 172.120