Whew, glad that's finally settled! Dave has declared Twitter "a waste of time." ;-) Had to tell you. Watch him tell Kevin Spacey in a video clip at Mashable.com. Just plain summer fun. [For readers outside North America, Dave Letterman is a very funny late-night talk show host on CBS TV.] Spacey offers to tweet something to his 800,000 followers for Dave and pulls out his phone. Dave asks how much … [Read more...] about Dave Letterman’s view of Twitter