Yes, I always followed the 3-day rule. We have no food allergies in either of our families, so I had no reason to be extra precautious; I was just being careful. I would definitely take your family history into consideration too; if you have a very allergy-prone family, I would be more vigilant about tracking every new food. But around 7-8 months, I stopped the baby food altogether and moved entirely to table food. It's easier for me not to have to make a separate meal for the baby, plus I find that I actually know more about what's in the food I give her now. When I give her apple, I know all she's getting is apple. And now that she's on table food, I'm not worrying so much about food allergies, other than waiting on things like peanuts until after her birthday.
Also, I was a little wary of the Gerber 2nd and 3rd foods, since they seem sometimes to include things that I'm not supposed to give them at less than a year (like some berries and citrus). So as you get into the mixed foods, keep an eye in the ingredients.