I have myself observed it, all the things b/w north and south are very different, may it be the language, eating habits and in terms of religion both consider themselves as Hindu but have different ways of expressing prayers.
Certain observations: 1. In south temples the prasada is different (mainly rice). 2. The deities are avatars of same God but quiet different like venkateshwara, tirupati which are not famous in north. 3. Eating habits(religious) like non veg is mainly eaten in south and rare in north. 4. in south temples everytime someone offers prasada to God, they lit the diya and ring bells and do short aarti.
There is a vast difference b/w the festivals, even same festivals are celebrated in completely different ways.
Marriage: In north people don't marry there cousins.
Kundali matching technique and precautions also different in north/south(not sure)
There is much more then this , mainly in north tulsidasa scriptures are preferred over old Sanskrit ones I think because it's close to Hindi, where as south Indians have different languages like Kannada, Tamil etc.
Tamil and Sanskrit both claims to be oldest languages of world.