Vaikuntha Ekadashi was celebrated on Shukla Paksha Ekadashi around the end of the English calendar. On this day, everybody gets to see Maha Vishnu through the open Vaikuntha door. All the Gods also get to see the Lord. This is the most auspicious and special Ekadashi among all the Ekadashis in the year.
Some people say that if we fast and perform pooja on this day with the performance of good Karma, we receive the fruits of performing the vrata on all the Ekadashis put together. It also assures the devotees a place in Vaikuntha after death. In all South Indian Vaishnavite temples, improvised Vaikuntha entrance is opened with a lot of fanfare and the Lord is brought out for the darshan of devotees. Then, post the Maha Pooja; the naivedyam is distributed.
On this day, in some orthodox Vaishnavite homes; the main door is decorated and a small idol of Maha Vishnu is brought out to perform a pradakshina with the Lord. They, then, take the idol back inside and perform special poojas similar to other Ekadashis.
This Ekadashi is called Putrada Ekadashi in North India. Childless couples fast often without water and pray to the child Lord Krishna for a progeny.