Vaikuntha Ekadasi: USA/Canada/Carrebian: December 16th 2010.
UK/India/Gulf, Australia: December 17th 2010.
Those who observe vaikuntha ekadasi on 17th in USA/Canada they are not observing it correctly. The earth isn't flat. If earth was flat then vaikuntha ekadasi would come to USA/Canada as the same date mentioned in indian calendar. But the earth is round and we have days and night.
Ekadashi finishes at 14:26 on December 17th as per Indian standard time. If you subtract. The new york time difference of 10 hours 30 minutes it will be the night of 16th and morning of 17th which is 3 hours 56 minutes. The rises in New york around 7:56 AM and ekadasi isn't visible on that day in New york. but it's visible at sunrise on 16th December and hence as per EST time zone it will be 16th December for New york but if you take the Central timezone then also it's 16th December same goes for other timezone. Basically in USA and Canada Vaikuntha Ekadasi is on 16th December and other parts of the world on 17th December. Even in Carrebian islands its on December 16th. Rest of the world -- 17th December.
if you have questions email me at shastriji at mypanchang com