Personally, for me, I wouldn't allow myself more than one every couple of days. Not because it might push me over my calories but just because I want to get out of the habit of having things like that. I don't really want to snack and if I'm going to, I want fruit etc. instead so it's more healthy. But then that's me, I know that I'm trying to remove these things and introduce them as an occasional treat so having one or more a day wouldn't really fit with my aim. So I guess you have to ask yourself, what is it you're trying to do? Do you just want to lose weight? Or is your attitude/relationship with certain foods not too great and needs fixing so you need to eliminate them and use them as a treat every so often? I think it's something completely individual so no-one can really answer it for you!
The good thing about calorie counting is that, strictly speaking, you could have 10 freddos a day and still lose weight. Unfortunately that would mean eating nothing else and would be seriously bad for your health!! But there is no recommended 'amount' as such. I usually eat one small bar of chocolate a day (freddo or milky way etc) as I find it keeps me on the straight and narrow with the rest of my diet. However, for some people that is way too much temptation and so they cut out chocolate entirely! As Caroline says - it's a good idea to try and wean yourself off things like this in favour of permanent healthy changes to your diet as you'll feel better for it.
Yummy as Morrigan said, technically if you are calorie counting you can have as many as you are allowed calorie wise, but you wouldnt have any thing else to eat and may feel a bit sick..hehe! But I always find if I have a week of eating healthy foods i lose more than if I eat bad foods even if the total calories are the same. But its definately not good to deny yourself of any treats because then you will want more!