Shathari

A) Satari is for Saranagati:

Saranagati to Lord Vishnu is the [COLOR=#0000FF !important]ultimate[/COLOR] surrender.
Sri Vedanta Desika composed 1008 verses of matchless beauty on the Lord’s sandals (Padakamala Sahasram), which support the divine feet; and all these in one night,
Mahabali had Lord Vishnu's feet on his head to get rid of his ego. Mahabali will be the Indra in the coming Manvantra. (Purandara is the [COLOR=#0000FF !important]current[/COLOR] Indra ),

In the Sri Satari, we can find the thiruvadis (two feet at the top of the Satari), which are said to be the feet of Srman Narayanan and this says that Sri Nammalwar is holding the Thiruvadi of Sriman Narayanan on his head.
Because of this only, we should bow down our head to get the Sadari on our head. And this is the regular custom that is followed in every Vaishnavite Temples.

B) Alavandhaar says in Stothra Rathnam:

"na dharmanishtosma nachatma vedi
na [COLOR=#0000FF !important]bhaktimaan[/COLOR] tvach charanaravindhe
akinchano naanya gathischaranya
tvath [COLOR=#0000FF !important]paadha[/COLOR] moolam sharanam prapadye"

"I am not religious; I do not know the nature of soul; Nor do I have any devotion for Your Holy Lotus Feet; Therefore, I am bereft- bereft of all good, bereft of any other shelter; Such as I- I, surrender unto Your LOTUS FEET.

C) 1. Why this Satari is being put on the heads of Devotee ?
Lord of the temple, an Archavatara murti, a form of Vishnu, whose feet are there in the Satari. Saranagati is placing the feet of Vishnu on our head. ([COLOR=#0000FF !important]Bharata[/COLOR] hold the chappals of Lord Rama). So Satari is placed on our head.

2. What is the procedure to be adopted by the Devotee while doing so by the Bhattar?
You lower you head and keep straight. Hold your hands in anjali posture.

3. What "sloka" to be recited by the Devotee at that time ?
Say Thivyaprabhantham, Thiruvaimozhi 5.7.1 or [COLOR=#0000FF !important]Alavanthar[/COLOR] sloka as above.

Or say "Sriman Narayana Saranav Saranam prapadye".

Or say ' Narayana' or 'Govinda'.

4. What is the difference between the 'Satar' so put in the Shrine of Lord Vishnu (The Main Deity, Goddess shrine and Other Sannadhis like [COLOR=#0000FF !important]Ramanujar[/COLOR] etc) ?
For the main deity the feet of lord Vishnu is on top of satari. Satari is different only in Vanamamalai temple. It has in addition to the Vishnu's feet, Nammalwar's Vigragam is also on the side. All other places it is the same with the feet of Lord Vishnu.

For Sri Ramanujacharya, satari is having the paduka of Sri Ramanujacharya. Sri Ramanujacharya's Paduka is called 'Mudhaliandan'. Sri Mudhaliandan was Sri Ramanujacharya's disciple. Sri Mudhaliandan's impeccable service to his mentor secured for him the status of being Sri Ramanujacharya's Padukas (sandals).

5. Why this procedure is not in vogue in Northern parts of India ?
The Vaikanasa or Panjaratra Agama Sastra is not followed in those places.
Source(s)

http://in.answers.yahoo.com/question/ind…