It's always in my fridge. It's a great accent flavour for Asian style stuff.
Michael G's recipe is similar to the one I use. I'll go soya sauce, rice wine vinegar (or lime juice), hoisin, chili sauce, grated ginger and garlic, sesame oil, veg oil.
The vinegar and oil you proportion the same way as when you're making salad dressing. The other stuff, you just use your judgment.
Alternatively, if you're making your own ketchup-based BBQ sauce, just put some hoisin into the mix. It's sweet stuff, so pull back on the brown sugar you would normally add to your sauce.