I will be shocked if it does happen on pentecost.  Reason being, is that Pentecost was already fulfilled long long ago, and according to the bible, the Lord Jesus Christ does not fulfilled the festivals of the Messiah twice.  All the spring feasts have been fulfilled, and I believe that there will be a whole ton of disappointments when we are still here after June 8-9th. 
However, I will not rule out the idea that God is in control, and he can make it happen as he sees fit for it to happen :)   But the scriptures do not point to Pentecost for the Rapture of the church... The hidden day, the day of concealment is on Yom Terrah, which is Rosh Hashanah.  Its also the day that NOBODY can know the "exact" day or hour that it is to occur on...
I am however open minded, and will be more than fully ready if Pentecost is the day that the Lord come and taketh us away :)