Edward Snowden via Glen Greenwald shed more light today on what he meant when he said given an email address he could wiretap anyone:
What's interesting here is seeing the actual NSA analyst search forms which are simple browser based applications. An analyst fills out a keyword, email address or website name (wildcards can be used) and select a search reason from a limited drop list, then clicks "submit" and he/she can find out a whole lot about you. This includes your web browsing history, online chats, emails, locations you've logging in from. All this is done without a warrant.