These threads always interest me. I try to give to charities throughout the year, and usually donate on the spur of the moment. (Obviously I have to have the dollars available, and there may happen to be one of the charities set up at the local shops or whatever looking for donations). I donate toys, clothes and books etc to the Salvos (or paraquad, or anglicare - the bins near my shops) throughout the year. I too look at what's for sale online and wonder how it's affected the local charities.
I got jaded regarding wishing trees as I found out one year (I never asked again) that my step children had received gifts from one. Their presents from their mother would have equated to $500 each and they had presents from their father and I as well.
But how do you determine who is "needy"? It's obviously a risk you take.