Ok, let me share my view after reading all these pages.
two points
1) There are pagan origins to some of these holidays like Easter,
Christmas ...etc
2) Today most (if not all) churches and christians who do celebrate
these holidays do so with a clear conscious that they are
remembering the birth, the suffering, death, resurrection of our
Lord Jesus Christ (at least I hope so).
Given the above 2 points,
What then should we do if we want to celebrate them?
I would like to susgest the following,
1) we need do it with a clear understanding of why we are doing
this, in that we are celebrating Jesus (and not Santa Claus/Easter
Bunnies).
2) also be ready to explain this to others where chances arise to
do so.
Is there any possibilities (however remote it maybe), that some
paganistic practices may slip into the church and hence corrupt it?
maybe.
Since not all believers are blessed with understanding (ie. mature
enough) in this area, some may be young and hence may be confused,
hence there is a need to be careful when celebrating these
holidays.
Personally, I feel that these holidays may well be a good
evangelistic opportunity for us to share the good news of the
gospels, who knows, people may get saved in this way.
God Bless. 
