Using a fresh address for each donation I believe is the right thing to do.
Static addresses on things like forum posts are fine, but when you can provide a fresh address it avoids issues where third parties analyze donation rates and sizes.
But for charity donations, wouldn't transparency be a good thing? When bitcoin becomes widely used and understood, organizations will have to weigh the pros and cons of a transparent financial structure vs a private one, or what combination to employ. I was hoping people would use the case of Wikipedia as an example. Should they offer a static address, and what would be the pros and cons?