•   Some people say that to kiss the hands and the feet of the pious people are prohibited and Shirk (associating partners with Allah). They say that by bending (like in Ruku) and kissing the feet of the pious we are making Sajdah to a creation of Allah Taala.
•   The Ahle Sunnah Wal Jama'at believes that this act is permissible and desirable as the books of Ahadith prove that the Ahle Bait and the Sahaba-e-Ikraam kissed the blessed hands and feet of the Holy Prophet (sallal laahu alaihi wasallam) and they even kissed the hands and the feet of one another.
•   The word Sajdah in the Shariah is meant that while doing Sajdah eight parts of the human body must touch the ground, namely both feet (toes), both the knees, both the arms (hands), nose and the forehead, with the express intention (Niyah) of doing Sajdah. Without the clear intention of Sajdah if a person lies on the ground by bending his legs and feet (as is susally done when some one feels extreme cold or he is inflicted with some ailment), this will not mean Sajdah. Therefore, to kiss the feet of the elders or pious persons is not Sajdah since it does not satisfy the conditions of Sajdah.
•   Sajdah is of two kinds:
  
  

•   Sajdah Tahiyat was permissible from the time of Hazrat Adam (alaihis salaam) to the Holy Prophet (sallal laahu alaihi wasallam). The Angels offered Sajdah before Hazrat Adam (alaihis salaam). Hazrat Yaqub (alaihis salaam) and the brothers of Hazrat Yusuf (alaihis salaam) offered Sajdah to Hazrat Yusuf (alaihis salaam). Later on, this Sajdah Tahiyah was declared as Haraam in the Shariah of Islam as well. Any one doing Sajdah-e-Tahiyah is guilty of a sin and committing act of Haraam. But he is not a Mushrik or a Kaafir. He can offer repentance (Taubah) in the presence of Allah.
   
•   As far as the question of bending before someone is concerned, this bending is of two kinds. If it is by way of respect to anyone, provided it is not to the extent of bending as in Ruku. If it is so then it is Haraam and Islamic Jurists have forbidden this kind of bending. The other kind of bending is while doing some other work such as picking the shoes with a spirit of respect. This latter posture is permissible (Halaal) as it has no tinge of worship.
   
•   When the Holy Prophet Muhammad (sallal laahu alaihi wasallam) visited the house of his daughter, Hazrat Fathima Zahra (radi Allahu anha), she would stand up for him in respect, take his hand and kiss it and make him sit in her place. When Hazrat Fathima Zahra (radi Allahu anhu) visited the Holy Prophet (sallal laahu alaihi wasallam), then he would stand up for her, hold her hand and kiss it and allow her to sit in his place. (Abu Dawood; Mishkaat Shareef)
   
•   Hazrat Abdullah ibn Umar (radi Allahu anhu) says that the Sahaba-e-Ikiram kissed the blessed hands of the Holy Prophet (sallal laahu alaihi wasallam). (Abu Dawood)
   
•   Hadrat Ashbah (radi Allahu anhu) went to the court of the Holy Prophet (sallal laahu alaihi wasallam), held the hand of the Holy Prophet (sallal laahu alaihi wasallam) and kissed it. The Holy Prophet (sallal laahu alaihi wasallam) said, "In you there are two habits which is dear to Almighty Allah and the Holy Prophet (sallal laahu alaihi wasallam)." (Adabul Mufrad) From this incident it is clear that the kissing of the hands is a desired action, which was even preferred by the Holy Prophet Muhammad (sallal laahu alaihi wasallam).
   
•   Once, two Jews came to the Holy Prophet (sallal laahu alaihi wasallam) and asked him a question. The Holy Prophet (sallal laahu alaihi wasallam) answered them. Thereafter, they kissed the hands and the feet of the Holy Prophet (sallal laahu alaihi wasallam) and told him that they bear testimony that he is a Nabi. (Tirmizi Shareef; Mishkaat Shareef)
   
•   A man came to the Holy Prophet (sallal laahu alaihi wasallam) and told him that he had taken a vow that should Allah Ta'ala grant Rasoolullah (sallal laahu alaihi wasallam) victory over Makkah, he would go the Holy Kaaba and kiss the chaukat. The Holy Prophet (sallal laahu alaihi wasallam) instructed him: "Go and kiss the feet of your mother. Your vow will be complete." (Umdatul Qaari)
   
•   Imam Ghazzali (radi Allahu anhu) states that Hazrat Abu Ubaidah bin Jarrah (radi Allahu anhu) kissed the hand of Hazrat Umar Farouk (radi Allahu anhu). (Kimya-e Sa'adat; Awaariful Mu'aarif)
   
•   Whenever the Sahaba-e-Ikraam would return from a journey they would embrace one another and kiss the hands of one another. (Bustaanul Arifeen)
   
•   It is said in "Alamgiri", Bab Mulaqatul Muluk, that if someone kisses the hand of a learned Scholar or the just King because of his erudition (learning) and the quality of justice with his people then there is no harm in it.
   
•   In the same book "Alamgiri", Bab Ziyaratil Qubur, it is said that it does not matter much if some one kisses the graves of his parents.
   

There are five kinds of kisses:
 

•   the kiss of affection and love like a father kissing his son,
   
•   the kiss of meeting (mulaqat) like a Muslim kissing another Muslim on meeting one another,
   
•   the kiss of love and regard like a son kissing his parents,
   
•   the kiss of friendship, when some one kisses his friend, and
   
•   the kiss of sensual love, like the husband kissing his wife or vice versa.

Some have added another kind of kiss as a mark of religious sanctity like of the Hajar-e-Aswad. (Alamgiri)
 

•   There is another kiss and it is in respect of religious sanctity and it is the kissing of Hajar-e-Aswad and the threshold of the Holy Kaaba. Some have said that kissing the Holy Quran is Bidah. However, it is reported that Hazrat Umar (radi Allahu anhu) used to kiss the Holy Quran every morning by holding it in his hands. Kissing the bread (roti) is permissible before Imam Shafaee (radi Allahu anhu) as a permissible Bidah or Bidat-e-Hasanah. (Durre Mukhtar)
   
•   It is now obvious that to kiss the hands and feet of the pious and respected persons is Sunnah and those who regard this Shirk and a Bid'at have no basis in their arguments.

Ref: http://www.nooremadinah.net/