The french grammar is the same for all french speakers world wide. I disagree with the previous comments saying it is a personnal choice. It means 2 different things so you do not have a choice you have to use the good one for what you mean. If you say - j'ai aimé ce film this means you see a movie one hour ago or 10 years ago and you liked it If you say - j'aimais ce film this means you liked the movie for a while and suddenly you stop to like it. If you are living in Provence maybe we could use a little more of french in our corrections ?

Can you give us some examples ?? As Zhigomar said, in lot of situations, you can't use imparfait in place of passé composé...

Like Guillaume said, you won't notice this phenomenon. I think, usually, it's a personal choice more than a regional convention. And sometimes people use imparfait just because they aren't sure about the participe passé of a verb :p

I don't think so, there are no so big differences in france, everybody speaks the same french in all the country, but in africa, it's possible they don't use excactly the same tenses than us. In much situations both tenses can be used, some people prefer on, some others prefer the other. Use passé composé with aimer/adorer can means that now it's finish, imparfait can means that can happen again. But, there are no differences of using tenses if you are in provence or in alsace.