I see no harm to using bitcoins for donations to churches however, I feel like it must undergo transparency especially to the public or to the congregation as this would promote fair use and monitoring of finances collected for the church to be used for charity works.  The challenge here too is that as the value of bitcoin is very volatile, the church may find it too difficult to monitor how much they already have and may complicate in the way they allot budgets for certain projects at church.  This for me works from a donor's perspective as it is truly anonymous and very convenient to donate whenever, wherever.  You don't have to go through the feeling of people looking at how much you're giving especially when those money baskets ate being passed around.