If I start using WeSync to access my primary calendar, does everyone on the Internet suddenly have access to all of my data?
No. You decide, right from your handheld, which resources are “publishable” and which are not. Then you also decide, within each of the communities you are a part of, which resources you want to publish to that group of people. That data only becomes available to those groups of people and is not accessible from other communities. Non-publishable resources remain local to your handheld and invisible to the WeSync Web site.