In the south, the festival is celebrated as Sri Krishnajanmashtami, Janmashtami or Gokulashtami.
In Tamil Nadu, Brahmins (Iyers & Iyengars), Yadhavas, Chettiars and Pillais celebrate the festival. Uriadi or climbing a stick containing a pot of sweet curds is also a major event in Varahur and other parts of Tamil Nadu.
The pooja is performed late in the evening, timed according to the Hindu calendar to coincide with the birth of Krishna at midnight. Generally, most of the sweets and savouries are prepared on that day. Normally, a Kolam (rice flour drawings on ground), also known as rangoli, drawn specially for the occasion, called ezhakoolam, decorates the front yard. Footprints representing those of Krishna are drawn from the front yard to the pooja room, representing the god entering the devotee's home
Infomation from wikipedia